Orton will definitely win for three reasons:
1. Orton has ZERO momentum going into this match. He got beatdown on Raw, then got pinned on Smackdown. Whenever a heel is booked like that leading into a ppv, they almost always win there since it'd be a "shock". How boring would it be if Orton gets destroyed all week, has no momentum, and still loses at the ppv?
2. If Cena wins, who is he going to fued with? Orton is the only main event heel and the next best option, Big Show, is busy tagging. Unless they turn HHH or HBK heel, Cena is out of big heels to fight. At least if Orton wins, Cena gets a rematch extending the fued to give time for DX to split and have HHH and/or HBK go after Orton as well.
3. Legacy have been a huge roll. So much so, that Orton almost looks like the weakest member since he's had more trouble with Cena than Legacy has had with DX. Since Orton's the leader, now would be a great time to be champion since his group have been doing great lately.
If the WWE are smart, they'll have Orton get the win here.