You guys seem set on AA, KK, AKs, but I wouldn't be quick to assume that. It looks to me like JJ or TT. I know he limped raised from UTG+1 but other than that he raises you about 4x your raise preflop, then really makes a protecting flop bet. It smells to me like a low overpair like JJ or TT. I think it's reasonably for him to think he is ahead. You raised standard from mp and did not reraise him. On the flop you could easily put him on a very strong hand and you did. So a strong bet will probably get a fold. There's no reason he'd put you on QQ. And maybe he limp raises JJ and TT so he gets more respect with AA/KK.
Is there some flaw in this reasoning?