KDR's post is right on. It seems to make the most sense for it to be Alex Wesker. He's got a cool backstory and I think everyone has wanted to play as Wesker in all of these games, hence why he is always in Mercenary mode. Capcom is delivering with this game. A new character that was introduced in the last DLC for RE5. It just makes sense. Was Alex brought up at any other point in the RE games that I don't recall?
If the whole game was only playable by kung fu guy, I wouldn't be happy. But with the 3 scenario approach it works. I'm looking forward to Leon's scenario more than any of the others, but I think all of them will be fun in the end. It will keep the game fresh throughout, having different playstyles.
Alex Wesker was added in the Lost in Nightmares DLC for RE5 one year after the original release... when this game was already being made. I think it's hardly a coincidence and the trailer points out the similarities with Albert Wesker quite frequently. Steve on the other hand was dead in the original CV, reconfirmed dead in Wesker's Report and once again in Darkside Chronicles. I think they've made it quite clear that he is, in fact, dead. His return would be pointless without Claire and we already know she's nowhere near this game. Also the T-Veronica does not grant those abilities as far as we know. Those are the same stunts Albert would perform and those were granted by the "special virus" given to all Wesker children. Also having Sherry and Alex as partners would be a nice nod to William and Albert.
Clearly there are many misinformed fans in this thread. Anyone who played RE Gold and actually can read knows that Alex Wesker is uber mega villain boss material not an ex mercenary interested in dough.
I am yours to command, point out our foes and step out of my way. - Adam, Shining Force