I think you have more than enough behind to get away from this hand. W/ the pot laying you 2:1, I'd say that he is more likely than 1:2 to have AK or AQ, less likely to have AJ if he is a decent player. My guess is he smooth-called the flop because he didn't want to give you automatic credit for an overpair, and then got a piece of the A on turn... A set is also possible here, and maybe he thinks you got a piece of the A and were planning a c/r on turn? Less liekly scenario is that he's overbetting pot to take out any weird straight draws.