brehs, the best most probable way for this to play out would be John Cena cashing in on Bryan
Thing is, Bryan won't be champion during the cash in. Punk will. It would still be during the progress of the match. Something happens that leaves both men out, or maybe Bryan does something to knock Punk the fukk out. Cena's runs in, FU's Bryan, 123.
there would be controversy cuz Punk will say he wasn't pinned, but Cena can claim that intejecting himself into the match and making it a 3 way was perfectly legal because he had the brief case, and of course Bryan can pull some slick excuse like "I had Punk right where I wanted him before I was attacked from behind by Cena
"
Summerslam 3 way..Cena wins of course, but at least we keep Bryan and Punk both in the main event