Of course they'll have a great match. No reason to think otherwise.
1. Cena retains without any kind of twist, and it's apparent that the whole purpose of it was to give Bryan a slight rub just by putting him in a match with Cena and get a five star match on Cena's title reign (just imagine if Cena beat Bryan by submission, lol. Internet rage would guarantee to entertain for months.) This would make no sense, of course, which doesn't necessarily mean it won't happen.
2. Cena wins, but unlike above, Bryan gets a rematch at Night Of Champions the next month and he wins the belt there.
3. Bryan wins, and then Randy Orton cashes in, possibly with Vince introducing him first (IF they do indeed want to turn Orton heel.) It'd be similar to the first ever MITB cash in at New Year's Revolution 2006, with Vince introducing Edge to cash in on Cena, except with Orton here. (It also makes sense given that Vince said last week on Raw that he'd prefer is neither Cena nor Bryan walked out as champ, that may have been a clue.) After Bryan wins the title, Vince could come out and give a short promo saying that if Bryan is so great, surely he can wrestle one more match, especially given it's against a man he's already defeated? It would be sarcastic and assholish in nature, since the answer is quite obviously No, he just wrestled the match of his life and pulled out everything he had to defeat one of the greatest ever in Cena, and Orton is very fresh and it's not like defeating Orton the first time was an easy feat to accomplish anyway.
4. Orton carrying around MITB and the possibility of a cash in (to those of us who think we've obviously already got it figured out) could simply be something to throw people off, and the match could just simply end with Vince screwing over Bryan himself without Orton being involved at all. The logic being that if Bryan isn't willing to change his image to better suit what a champion of his company should look like, then Vince will do what he can to keep the belt from him.
5. Bryan wins, and there's no screw job, just him raising the title in the air with the whole crowd chanting YES along with Bryan. Orton could cash in and FAIL, but I would hate that.
I could honestly see any of the above options happening except option #1.
