One of Cena's main slogans is "Never Give Up", which would also imply never tap out, I'm sure. As historical as it would be for someone to finally defeat Cena by submission (the commentators will try to sell it as if Cena has never tapped at all his entire career), fans chant "You Tapped Out" even when huge baby faces like Triple H and Randy Orton give up, now imagine the kind of reaction someone like Cena will get for tapping out. WWE isn't gonna want that. Most likely, Bryan will slap the Yes Lock on Cena and they'll linger on it for quite awhile, having people believe that Cena is actually about to submit, but then he manages to break out of it.
I've said this many a times, but I think Bryan is gonna get into a series of different kind of pin fall maneuvers and eventually he'll get him that way. As mentioned, Bryan is known as Mr. Small Package to many and he's won matches the last two weeks (against Caesro and last night, Kane) with that move so I think that's how it's gonna happen.