It's official: Marvel vs. Capcom 3 trailer
On the Marvel side there's Wolverine, Iron Man and The Incredible Hulk.
Also, in one of the shots it looks like Chun-Li's outline, so she's almost certainly in the game as well.
Thanks to Rorshock520, 1st2nd3rd4th, keNzo, Dekew, SWK, Andyman, Roman4328, Clovr4Lyf and Bluith for pointing the trailer out.