I say, slowly turn Cena heel as champion (especially now that National Make a Wish day is over). Make him ego driven, annoying and try to get the kiddos that cheer him to boo him. He spends the majority of the Summer as a heel, refusing to take matches, etc. At the start of their SS programs, have CM Punk return being the guy that was the biggest thorn in Cena's side. Punk comes back as a monster babyface, Cena is now positioned as the #1 heel in the company, leading up to a CM Punk v Cena Title match at SS.