I've got no leaked footage to confirm anything on this. No anonymous tipsters, no website code hacking. What I do have is Capcom's Niitsuma-san, the producer of Marvel Vs. Capcom 3. Over at Capcom Unity, you can check out a recording of yesterday's MVC3 livestream, which includes an interview with Niitsuma starting around the 8 minute mark. But the interesting bit comes in after 20 more minutes, where attention is brought to the new stages being shown. On this, Niitsuma comments (via interpreter):
Yeah, here at Comic-Con we're showing off the S.H.I.E.L.D. helicarrier stage, and the Resident Evil stage. And the reason for these stages - we had in mind, instead of just having random places to fight, each stage is tied into some of the characters in the game, so as you saw from what we have released here, like Chris Redfield, Resident Evil character, so Resident Evil stage, and the S.H.I.E.L.D. helicarrier ties to some of the other characters in the game. So that was the goal behind that - we'll be seeing more in the future.
About 8 minutes later, Joveth "jgonzo" Gonzales asks explicitly about the Mega Man Legends themed stage in MVC3. Niitsuma answers:
People who spotted that stage in the game, they've got some good eyes. I don't want to go back on what I said before, about characters and stages, so just keep your eyes out for the upcoming trailers and you'll see.
While it's nothing official, per sé, the conviction seems pretty strong that a Legends based character has a good shot at entering the game. Of course, Tron Bonne is already no stranger to Marvel Vs. Capcom, but ultimately we'll see what's announced.
Thanks Joveth. :)