If ManU beats ManCity and Barca advances to the final, than yes, it will happen. Even if R. Madrid advances to the final, it might happen. I think on neutral ground R. Madrid will definitely beat them but they're in their own country at Wembley, where they've played plenty of times. Has a team ever lost the Champions League final in their own country?
I'm shocked people are saying "it is indeed possible" and ManU "can win the treble..." Obviously they can win it, it's not a discussion of can it's a discussion of will. They won the league, they're favored to win on Saturday and if they do the FA Cup is in the bag, and they secured themselves a place in the Champions League final (the draw sure helped, as I predicted it would). It'll be 90 minutes determining whether or not they win the treble, and 90 minutes at home against a team they are perfectly designed to beat (especially if it's Barca). I'd place a huge bet right now on ManU winning the treble.
When they do if anything it only speaks to how great a manager Ferguson is. This ManU team is a team in transition and they're not as good as they have been in recent memory. But the Prem was pretty weak this year, so they got those two trophies, and they had a very easy route to the final An easy group followed by Marseille, an out of form team that's not so good this year and fighting for a champions league place, and a Schalke team who just changed managers and is in 11th place in the Bundesliga? Then getting to play the final in your home country's national team stadium, where you've played a lot of games? The cards were on their side.