It's official, Marvel vs. Capcom 3 is in development. From the trailer on the Capcom side you can see, Ryu, Morrigan (Darkstalkers) and Chris Redfield (Resident Evil).

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.

Marvel vs. Capcom 3 Teaser Trailer