Honestly, there's a lot more Edge could do right now with the WWE Title than Cena can, and that's because the talent is so lop-sided in WWE right now on Raw. On Raw, nearly all of the top players are faces... you've got Cena, HHH, Shawn Michaels, Kane, Ric Flair, Carlito, and even Jeff Hardy could be thrown in. Edge could easily have a HHH type run, going up against one face after another and Edge could theoretically be busy for at least a year just facing all of the active faces on Raw.
Of course, not many people enjoy year long reigns, I don't myself, but that's beside the point. Back to the topic at hand... Cena won't have much to do and the top heels on Raw are Edge, Randy Orton, Umaga, and you could throw in Chris Masters. The problem is everyone is sick of Cena and Edge, so if Cena wins, that won't happen again. Cena and Randy Orton is not going to start unless it's build up for a Wrestlemania and there's no way Chris Masters would ever get over in a singles fued against Cena for the title. Maybe non-title, but not for the WWE title. On the other hand, Edge is such a hated heel that everyone he faces would get huge face reactions, so it's less of an issue than with Cena.
What you'll see is this.
Cena wins the WWE Championship at Unforgiven. Somehow, Umaga will become the # 1 Contender for the WWE Title, heck, he'll probably just come out to attack Cena one night and all will be set. Cena will face Umaga at Cyber Sunday, and since there's really no one else title worthy besides Orton waiting, Cena will go ahead and face Umaga again for the WWE title at Survivor Series. At New Years Revolution to start next year, I will not be surprised at all to see yet another Elimination Chamber that'll probably feature Cena defending the title against 1) Edge; we'll be reminded in January about how he is a 2 time WWE Champion as if he conveniently just now remembers it, and seeing as how he was Cena's opponent all of this year it makes sense...2) Umaga; why not, since he will likely be Cena's opponent for the last couple months of the year... 3) and 4) HHH and Randy Orton; it's likely that HHH and Orton will cross paths at some time and their fued will be thrown into the Chamber to fill it out and 5) Shawn Michaels because well; he's Shawn Michaels.
All signs indicate that Cena retains and somehow Orton becomes # 1 contender for Wrestlemania... there's your WM23 main event.
I'd prefer Kane make a heel turn and title run, but I've given up on WWE using Kane the right way.