[rwanger]

Check and hope he doesn't push.

You may have to call a bet from him on the river though. Some people will probably suggest a block bet, but with 7.5k in the pot, you'd have to bet 2k or so, which would commit you to calling a raise.

The only way you aren't behind here is if he had a weaker Ace. AK, a set, and diamonds all have you beat.

Be wary of getting involved like this against one of the few players who can bust you. Although, then again, your stack isn't THAT big compared to the rest of the table.

Based on how he has been playing, you'll have to think about this:
If you check and he pushes, are you going to call?

If yes, then you might as well push yourself, since he'll probably call with a weaker Ace, but doesn't really have any reasonable drawing hands that missed and he'd have to bluff with.

This is not an enviable spot.

If you check and he pushes, you're getting over 3:1 right? It's going to be hard to lay that down, because if you win, you'll probably lead the tourney. If you fold, you'll have 15BB's.

You might have been better off playing the earlier streets differently. What about pushing the turn? He very well might call with a weaker Ace. He probably won't call on a draw. He'll call if he has you beat, but you were going to have a hard time getting away if you you were beat anyway.

If you ignore stack sizes, you bet the hand just fine. Considering the sizes though, you probably would have been better off keeping the pot smaller (smaller bet on the turn, although that unfortunately looks weak and he might make a play), or commit yourself earlier in the hand, because really, at this stage of the tournament, you're probably going to have to assume that AQ is good in this spot. Don't give yourself a chance to make a mistake on the river (by folding the best hand, or calling after he hits his flush).