I wouldve done it at wrestlemania 25 john cena vs edge w/vickie guerrero (sorry, no big show). during the build edge says he wants to prove cena wrong and that he doesnt need help to beat cena, cena says he is SICK of everything edge has done to him in the past, this gives hints of edge being noble and cena being aggressive. and then during the match the match, vickie guerrero low blows edge behind the refs back helping cena win telling the story of what fans had been murmuring 'cena being protected by management'. a double turn that also turns edge face giving cena a hero to fight. like austin vs bret, edge could become the anti-hero
