We'll treat this as a rumor for now, but it may not be for much longer. The above New York Comic-Con image comes 4chan, apparently originating from Eventhubs.com, revealing Mega Man, among some other characters, in Marvel Vs. Capcom 3. Making matters shadier, Eventhubs pulled the images soon after. The consensus is that the characters are being held for a Sunday reveal.
Of course, Mega Man is a Marvel Vs. Capcom veteran, and his inclusion would probably come as no surprise. Additionally, this wouldn't even be the first MVC3 leak that's come out of New York Comic-Con already. Be that as it may, we can only still speculate for now.
Edit: We are aware that the artwork comes from Marvel Vs. Capcom 2, but it remains to be seen why it's been posted at NYCC at all. If all else we can ask Joveth about it on a podcast or something, hahaha.
Edit 2: I've been informed that these pictures do not come from Capcom's booth, but rather IGN's booth. Why they would advertise MVC3 with MVC2 art is certainly unknown, but it takes away the officialness of the images.