3-bet or call the raise on the flop with the nut flush draw?

[Guido]

Party Poker 1/2 (10 handed). Loose/ pretty passive table (just what I like [img]/images/graemlins/smile.gif[/img]).

Hero has A[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/heart.gif[/img] and is UTG

Hero limps, EP1 limps, EP2 limps, MP3(poster) checks, CO limps, Button raises, arg, blinds fold, all call.

Flop(14 SB): 2[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/heart.gif[/img]

Hero bets, EP1 calls, EP2 calls, MP3 folds, CO calls, Button raises, Hero 3-bets, EP1 folds, EP2 folds, CO calls, Button calls

Turn(12 BB): 8[img]/images/graemlins/heart.gif[/img]

Hero bets, CO calls, Button calls

River(15 BB): Q[img]/images/graemlins/spade.gif[/img]

Hero bets, CO folds, Button folds

My question is: should I 3-bet the flop or just call? What would your play be after that?