The Rachel McAdams capers

Playing an ambitious blogger in 'State of Play' and the inamorata in a new Sherlock Holmes film is all in a day's work for Rachel McAdams. The actress talks to Lesley O'Toole

After Diane Keaton starred with the Canadian actress Rachel McAdams in 2005's The Family Stone, she was moved to announce: "I hadn't been that impressed with someone since I worked with Meryl Streep." Most of Hollywood was already thinking that way. In 2004, McAdams's consummate mean girl in Mean Girls almost stole that film from its putative star Lindsay Lohan, then the girl Hollywood was starting to lose sleep over. The same year she starred with Ryan Gosling in the surprise hit The Notebook, a swooning old-fashioned love story not hurt by its stars' on- and off-screen passion. And then she was Owen Wilson's effortless, utterly appealing dream girl in 2005's comedy hit Wedding Crashers.

This year, with three high-profile films due for release, the 30-year-old McAdams is at last unleashing herself properly on the world. The show might seem orchestrated, but it is not. "The timing of these things is so strange," she says. "You can go from tundra to tumbleweeds."

The first of these is State of Play, Hollywood's version of the acclaimed 2003 British television miniseries. The film was first slated as a Brad Pitt vehicle before he dropped out during the 2007 writers' strike. Russell Crowe replaced him as the old-school, mostly good guy, Washington, DC print journalist whose duelling friendships with a Congressman in peril (Ben Affleck) and a young online blogger, played by McAdams, collide quite spectacularly. Then, this summer she will star in the long-awaited film of the book-club favourite The Time Traveller's Wife, opposite Eric Bana. At Christmas, she's in Guy Ritchie's Sherlock Holmes with Robert Downey Jr and Jude Law.

Most often termed "the new Julia Roberts", McAdams seems poised for a place in a more searing kind of sun. "I'm feeling a little bit bashful about it all, to be honest," she grimaces, having arrived for our Beverly Hills appointment without a publicist in tow (unusual for "talent" of her station) and with a low-key, friendly demeanour, also not especially common among actresses of her level. "It's all a little bit big and scary. Sometimes, you can make it really big in your mind but you have to take a breath and calm down. And take it one step at a time. But I think I'm ready. Hopefully, I won't have a meltdown."

She's certainly bided her time, turning down career-enhancing opportunities galore – Anne Hathaway's role in The Devil Wears Prada, Eva Green's in Casino Royale, Gwyneth Paltrow's in Iron Man – and not obsessing about a lean couple of years release-wise. Clearly, she does not feel that Hollywood urge to be in the spotlight whenever conceivably possible. She even turned down a Vanity Fair cover – to be shared with Keira Knightley and Scarlett Johansson – when they asked her to pose nude. McAdams just didn't feel the need.

No wonder, then, that she's slightly blasé about her actual and potential State of Play co-stars. "I'd have been quite happy either way," she says, laughing, of the Brad Pitt/Russell Crowe choice in the role of her mentor.

She does, however, admit to some pre-shoot jitters over Crowe's professional reputation. "I was really nervous. I'm always a little intimidated when I'm working with a great actor who has a well-known persona and you don't know what you're walking into. But then I felt the same way with Helen Mirren [who plays the newspaper's editor]. It was like, 'Oh my God! It's Helen Mirren!'

"I actually met her and Russell at the same time. They said, 'We'd like you to come to a little meeting, just with Helen Mirren and Russell Crowe. Nothing special.' I was terrified. So I tried to have a good breakfast. I got up and did yoga. I'm obsessed with kundalini. I practised my breathing techniques. I still get really nervous and kind of shy. I was still shaking when I walked in and shook Russell's hand. I'm sure he noticed, but happily he didn't say anything."

For the purpose of verisimilitude, the producers arranged a cast trip to the Washington Post newsroom. "I just didn't know how any of it worked," McAdams says. "It was so interesting being a fly on the wall in those morning meetings: 'What's everybody got? What's in the pipeline? Oh, that's dead, nobody cares about that.' And the things that people really cared about hearing about.

"Also, it's such a politically minded newspaper and we were there at the time of the elections. There was quite a frenzy going on. I know for sure now that I could never have been a journalist; I just couldn't handle the pressure or deadlines."

That said, McAdams and two friends have set up an environmental website, called greenissexy.org. "I had a friend who started working at an organic café. She invited me along one day, and there was a certain energy that piqued my curiosity. Plus, I felt like I'd actually had quite a disconnect with the planet while growing up. I'd go to the beach all bundled up with a turtleneck on and sit there and read my book and scowl. But then, I hadn't been seeing the most beautiful beaches in the world. Then I went backpacking in Australia and rediscovered my passion for the planet."

Home now is Toronto, where McAdams recently bought a house, or wherever her actor boyfriend Josh Lucas is. She was raised just outside London, Ontario; her father was a truck driver and her mother a nurse (she has a younger brother and sister). From the age of four, she excelled at ice-skating and competed for years. She did well at school, dabbling in plays and fancying cultural studies as her degree subject until her drama teacher suggested she consider theatre. She graduated with her degree in fine arts from York University, Toronto, soon started work in television and made a couple of films, and then came The Hot Chick.

She has a quiet confidence in her own skill, though no hint of cockiness. Does she feel her talent justifies her hype? "I guess it's one of those things where I don't know if I'm good at acting, but I have a certain capacity for it. Sometimes, six hours will go by on a set and I won't even notice. Or the day's over and I'm like, 'I haven't eaten anything all day.' I was listening to [the New York Times podcast] Tech Talk and this guy was talking about flow in work and when you're passionate about something you kind of get into a groove and the world sort of melts away. That seems to happen to me when I'm working on a set."

She most recently completed filming Sherlock Holmes in and around London. "It was so advantageous to shoot in the place Arthur Conan Doyle wrote about. At one point, we were in an actual dungeon covered in Victorian sludge. The walls were dripping. It was really quite authentic. It's also a really big movie, the biggest I've ever done. There were grandiose sets and beautiful, stunning costumes – head-to-toe satin and bustles and corsets."

McAdams said recently that, her own love story with Holmes aside, the film is a love story between Holmes and Watson. She runs her fingers through her curly brown bob (she's a natural blonde) and laughs in a resigned way. "I'm going to get it for that, but you'll see what I mean when you see it. They have developed a lovely relationship of camaraderie."

McAdams must leave for an appointment with her stylist "to put nips and tucks" in her dress for the Los Angeles premiere of State of Play. Getting red-carpet ready is not, she insists, something that comes naturally. "I think my attitude to the whole fashion side of my job is the same as the acting part. I'm kind of open to anything. I love variety. I don't have a favourite designer [here, she is wearing Catherine Malandrino]. I most love my cowboy boots. They're Wrangler!" Julia Roberts would be proud.

'State of Play' opens on 24 April