^^^You all but answered your own question.... From the current Raw roster it would obviously be Punk to step up into the ME.
That said, there's no immediate need if Cena remains champ... Rather than faces, if Cena retains beyond WM more heels would be required.
I share your lack of desire to see Punk/Cena though... Well, that is at least until such time that they've built him up enough to be a
plausible challenge for the man from West Newbury anyway. Right now, in kayfaybe, Cena/Punk would be a total annihilation.