The Toffees have lost their last five games, three of them under caretaker manager Unsworth, and sit in the Premier League relegation zone.
Unsworth left Rooney, Leighton Baines and Phil Jagielka at home for Everton's 3-0 loss to Lyon on Thursday, which ended their Europa League qualification hopes.
All three are set to be involved on Sunday, and Unsworth said: "Senior players are always important and they're all top players with many appearances under their names.
"We've got a few young players in and around the squad as well so their importance to those young players is vital. Any time you go into big games, and Sunday's a big game, a cup final for me, you always need your senior players who you can rely on and trust."
After a seventh-placed finish last season and a summer of big spending, expectations among the blue half of Merseyside were sky high, making their current difficulties all the harder to swallow.
Unsworth, who has stepped up from the under-23s and is hoping to be given the job on a permanent basis, believes Everton's problems are collective.
He said: "It's very difficult. For most of the games I've been in charge we've competed, the effort's there. Occasionally we've made silly mistakes that have conceded goals so we need to tighten that up.
"We need to try to create a few more opportunities to give everybody the opportunity to try and hit the back of the net.
"It's a little bit of everything and you try to tweak that as best as you can and you try and pick the best team and individuals for the next game, because all that matters is winning the next game."
Watford have been another surprise package this season but for much more positive reasons.
Marco Silva has been linked with the job at Goodison Park after guiding the Hornets to eighth place, racking up three wins from five away games.
Unsworth has called on the Everton fans, who grew increasingly vociferous in their opposition to previous manager Ronald Koeman, to ensure there is home advantage.
He said: "We stick together, and that includes the fans as well.
"The players have got to play on the front foot. They're well aware of what's needed at Goodison and, if they're not, I'll certainly be reminding them. We need to try and play with freedom and positivity and that's my job to instil that in the players.
"Goodison is an amazing place to play football. I know it like the back of my hand. When our fans get behind us there's no better place.
"I know on Sunday that they'll be there for us. Not me, but for the team, because the team needs its fans at the moment and we all need to stick together in a difficult time.
"We need to win a couple of games quickly, because my experience playing in the Premier League tells me that you can go and win a couple of games and all of a sudden be in the top 10."
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies