I'm not entirely familiar as to how does imdb update their contents or information (I mean, if it's a wiki or something else), but if its info is reliable, we have 2(3) new characters announced (though probably just NPCs), as well as some voice actors.
Steve Blum ... Wolverine (voice)
Robert Clotworthy ... Mr. Fantastic
Robert Tinkler ... Speedball / Penance / Nova
Kiff Vanden Heuvel ... Crowd members
http://www.imdb.com/title/tt1266580/
EDIT: By the way, I got this information from here: http://www.gamespot.com/xbox360/rpg/marvelultimateallianceiifusion/show_msgs.php?topic_id=m-1-46080278&pid=951211
someone is playing songbird and dagger: Susan Spano ... Songbird / Dagger / Announcer (voice