The festival celebrates the Canadian city's long-held love for big tops, acrobats and high-wire extravaganzas

The time? Around 9.15pm on Saturday 10 July. The location? The corner of Rue Saint-Denis and Rue Ontario in the Plateau de Mont-Royal. The event? Well, that's not entirely clear just yet. We'll just have to wait and see.

The Plateau is one of Montréal's most desirable districts. The houses here have smart 19th-century red-brick frontages and wrought-iron balconies. There are plenty of boutiques to browse through and fine restaurants in which to dine. In fact, I had to rush dinner in La Fabrique – a tiny but popular place with lots of exposed brickwork and a fine line in pan-seared cod – and jog a couple of blocks down Rue Saint-Denis to be here on time. Along with a few dozen others, I've been drawn here on the understanding that "something" is going to happen. Local radio has hinted, the virtual world has Tweeted – but the organisers are keen to maintain secrecy, so we're all pretty much in the dark.

That darkness is suddenly interrupted by a burst of wavering light further down the street. There's some sort of commotion going on over there. We're all on tip-toes, craning our necks, but it's hard to see. Is that cheering we hear, or wailing?

From this point on, everything moves pretty fast. A squad of highly charged young men and women in white shirts and black suits are suddenly among us, operating in strange synchrony: in unison they crouch, or start cheering, or jump up and down, or laugh, or stand motionless. Each has a bright torch which they periodically wave in the air. Not so much a flash mob, more a flash-light mob.

Suddenly everything stops. The new arrivals train their torches on the vacant space above a one-storey shop-front, where an extremely well-toned man begins a series of balances and holds, accompanied by a crackly soundtrack emanating from some old stereos perched on the roof-edge. It's balletic stuff, an exercise in physical control. As he raises his body upwards on a single hand, does the splits, and wheels round on a series of wooden posts, the flash-mobbers move among us with hand-held radios broadcasting the same music we're hearing, giving everything an eerie, surround-sound quality.

A banner is unfurled: "Les Minutes Complètement Cirque", it says. The man disappears through a first-storey window; the flashlight people disappear into the crowd.

Roll up, roll up! The circus is in town. Or rather the circuses are in town. Montréal Complètement Cirque is the first edition of what will be an annual festival in the city, with troupes arriving from all over the world to dazzle local audiences with athletic virtuosity, juggling talents, acrobatics, dancing skills and general clowning around.

But then again, the circus is always in town in Montréal. The world-conquering Cirque du Soleil was founded here in 1984 by two street performers called Guy Laliberté and Daniel Gauthier. Now it has 20 different shows in performance around the globe, from Las Vegas to Tokyo, and employs 2,000 people in Montréal alone. Cirque du Soleil's touring shows are always premiered here, and during most summers the troupe's state-of-the-art big top dominates Montréal's old port area, the friendly blue and yellow stripes on the outside disguising a hi-tech, air-conditioned interior.

As a result of this success, other Montréal-based circuses have sprung up: Cirque Eloize and Les 7 Doigts de La Main are both performing at this year's festival. The former has a big top of its own showing ID, an edgy blend of street performance and acrobatics, while the latter is presenting an elegant cabaret-style event at Montréal's gracious Olympia theatre.

ID impressed me the most, with much parkour-derived leaping around over the set, a stunt-cyclist, and a final "skip-off" between two rival gangs of acrobats and dancers: a West Side Story for the double-jointed. However, both prove that there's an impressive depth to the art form. This isn't PT Barnum stuff, with sawdust-covered floors, animals being forced to do desperate tricks and a risk of imminent death for the performers. Cirque de Soleil pioneered a contemporary circus style that blends dance, circus and street performance to create a spectacle that concentrates on grace, drama and rhythm as much as it does awesome physical feats. Safety is paramount: discreet harnesses are used and padded mats save the performers from doing themselves the ultimate injury.

Montréal also has its own circus district – La Cité des arts du Cirque – set in Saint-Michel, a hitherto run-down area to the north of the city centre. Here the hi-tech headquarters of the Cirque Du Soleil combine with the National Circus School and a permanent performance area called Tohu to enhance the city's circus credentials. According to Howard Richard, who rejoices in the title of Director of Creation at the National Circus School, "We're focusing on developing well-rounded circus artists, not just to be good at one discipline, but to be versatile. They need to participate in the entire process on a creative level."

Crikey. It's all a long way from pratfalls, red noses and big clown feet. The surprise is not that the city has a circus festival, but that it hasn't had one before now.

But perhaps that's because circuses aren't the only trick Montréal has up its sequin-spangled sleeve. Canada's second-largest city (after Toronto) thrives on festivals. The International Jazz festival is one of the biggest annual events, and this year's circus festival has to contend with the lure of the Fantasia animation festival, a summer-long fireworks festival, the African Nights music festival, and the huge Just For Laughs comedy festival. With all those other distractions available to potential audiences, who'd want to be a trapeze artist?

Not me, I can now conclude. Cirque Carpe Diem runs the Trapezium Flying Trapeze Centre in Montréal, where visitors can get to grips with whizzing through the air. However, for the duration of the festival they've also set up an outdoor version near the imposing cylinder of Tohu in the circus district, where locals and tourists alike can have a go for a mere C$5 (£3.30).

A man called Billy from Tennessee showed me the ropes. They looked awfully high up. "We're going to try the leg hang," he said. "Just do what I tell you." We did a 20-second dry run at ground-level, then I was being clipped to a safety harness and sent up a rather long ladder. The hardest part is just grabbing the trapeze itself, which threatens to pull you off into the abyss as you cling to it. Happily a friendly chap at the top held me by the waist until the appointed moment. Then I was off.

It all goes by very fast up there: quick, get the legs hooked over the bar; let go the arms; ignore the fact that your T-shirt is sliding off and the blood's rushing to your head. Then it's hands up again, legs dangling. Someone shouts at me to do a back flip. Back flip? I collapse on to the netting in a heap instead. Juggling's probably more my thing.

Even without the circus fixation, Montréal is a peculiar place. The largest city in Québec, it is perched on the largest island of an inland archipelago in the Saint-Laurent river and was once the gateway to a roaring trade in beaver fur. As a former French colony its heritage is predominantly Gallic, yet it seems to oscillate between European and North American sensibilities in an instant. Not just the language – most Montréalers are bilingual, although French is the official language of street signs and restaurant menus – but even the architecture of the city reflects this peculiar balance.

The streets of Old Montréal could easily pass for those of Nice or Paris, with various tiny boulangeries and boutiques hidden away round picturesque corners. The narrow Rue Saint-Paul is strung with smart little shops, while cafés and restaurants line the wider Rue de la Commune. Place Jacques Cartier is a bustling public space bordered by historic buildings such as Chateâu Ramezay, once the home of the French Governors and now a museum of Québec history. Some of the streets here even have cobbles.

However, as you head into the Downtown area, the cobbles give way to a grid system, the older buildings become isolated among modern office areas and 19th-century red brick. Everything becomes more direct, more imposing, more modern, and finally brick gives way to glass and steel.

It all comes together in one place: Place d'Armes, where the Gothic revival facade of the Basilique Nôtre-Dame stands next to the oldest building in the city, Saint- Sulpice Seminary, which dates back to 1647. Both face the Bank of Montréal, modelled after the Pantheon in Rome and built in 1847, while on the west side of the square the dark-glass skyscraper of the National Bank of Canada faces the dramatic Art Deco heft of the Aldred building.

And that's just on the surface: to add to the city's peculiarity a staggering underground system of malls and 30km of corridors link buildings, museums and the metro system below ground so that locals can get around the city in the depths of winter, when two metres of snow can fall in a single season.

It's little wonder that Montréalers like to get outside in the summer. Perhaps that also explains their intimate relationship with the bicycle. In the continent of the car, bikes are king here, with 450km of bicycle lanes to choose from on the island, as well as a new "Bixi" public bicycle sharing scheme. The concept has proved so successful that many of its principles have been adopted by London for its version, launching later this month.

Pedal north from Old Montréal and you'll discover the city's green side at imposing Mount Royal. Here, gentle parkland slips past three vast and sombre cemeteries; the views over the city stretch far beyond the bizarre-looking 1976 Olympic Stadium. Alternatively, pedal south around the old port and you'll reach to Parc Jean-Drapeau, which spreads out over the isles of Sainte-Hélène and Ile Nôtre-Dame in the Saint-Laurent river. These quiet islands, linked to Montréal itself by the brutal span of the Pont Jaques-Cartier, are themselves relics of previous Montréal festivities. Sainte-Hélène was increased in size and Ile Nôtre-Dame was created from the spoil formed during the construction of Montréal's Expo 67. V CIle Nôtre-Dame's curvilinear French pavilion also dates back to the Expo; it's now a casino encircled by the Gilles Villeneuve F1 race track, itself open to all-comers. Even cyclists. So I selected my most racing gear and had a crack.

It's a strange experience navigating a 4.3km Formula 1 racing circuit on a bicycle. At one point I was overtaken by a local bus (which was nevertheless observing the strict 30km/h speed limit). Rubens Barrichello apparently managed to zip round in 73 seconds in a Ferrari in 2004. My personal best came in at a leisurely 17 minutes, including pauses for photography.

Whether you walk, cycle, drive or take the Métro, the central districts of Montréal reveal contrasting sides to the city. Boulevard Saint-Laurent is Montréal's historic dividing line between the eastern (historically largely Francophone) and western (Anglophone) areas.

Slap-bang in the middle, though, is Schwartz's Hebrew Delicatessen, which prides itself on not changing a thing since it opened in 1928. It's packed at lunchtimes, with queues stretching way out the door, and once you've got a table, the choice is basically a smoked meat sandwich or a smoked meat sandwich.

"The chicken sandwich is off," said a waiter. "We've got turkey, but to be honest it's not that special." Happily, the smoked beef sandwich – served with pickle and fries – tasted just fine.

From Schwartz's, head south and you'll eventually hit Rue Sainte-Catherine, which runs east to Montréal's gay village. Much of its length is pedestrianised during the summer, with plenty of bars and shops to choose from.

And, somewhere, there's probably a circus performance going on. Sometimes it can be disturbing. A case in point is Tabú, currently being performed by the Welsh company Nofitstate at Tohu: deranged acrobats in quasi-Victorian costumes whizz around on pulleys above an audience that has to move around at the whims of the players. But sometimes it's all for fun: one evening a freight train pulled up in the old port, with jugglers, trapeze artists and clowns entertaining the crowds.

For practitioners of such an upfront art form, Cirque du Soleil operates with a very high degree of secrecy. Within its headquarters the concepts for shows are decided, costumes are created, performers are trained, wigs manufactured, fabrics dyed, music composed, and big clown shoes are cobbled together – all away from the prying eyes of the general public.

However, the Willy Wonkas of the circus world have now allowed some of their costumes to go on temporary public show at the McCord Museum in the Downtown area, at an exhibition which runs until 11 October.

The designs and the attention to detail are extraordinary – and almost all their shows are represented – but it's strange to see costumes designed for such active, supple performers draped over motionless mannequins. The big top is where these garments belong. You can almost smell the greasepaint.

Travel essentials: Montréal

Getting there

* Air Canada (0871 220 1111; ) and British Airways (0844 493 0787; ) fly daily to Montréal from Heathrow.

Staying there

* InterContinental, 360 Rue Saint-Antoine Ouest (001 514 987 9900; ). Doubles from C$220 (£147), excluding breakfast.

Eating there

* La Fabrique, 3609 Rue Saint-Denis (001 514 544 5038).

* Schwartz's Hebrew Delicatessen, 3895 Blvd St-Laurent (001 514 842 4813; ).

Getting around

* Ca Roule Montréal (001 514 866 0633; ). Bikes from C$8 (£5.35) per hour.

Visiting there

* Tohu, 2345 Jarry Street East (001 514 376 8648; ).

* Trapezium, 2350 Rue Dickson (001 514 251 0615; ). Lessons from C$40 (£27).

* McCord Museum, 690 Sherbrooke Street West (001 514 3987100; ). Admission C$13 (£9).

More information

* Montréal tourism: and

* Montréal Completement Cirque:

* Cirque du soleil:

* Cirque Eloize:

* Les 7 Doigts de la Main: