20$ -1 add on/1 rebuy KQ top pair

[brea]

I had seen the villain flop top pair (Queens) with the nut flush draw two hands prior and not bet until the flush fell on the river. He flat called in the big blind in this hand. Whats my play here?

PokerStars No-Limit Hold'em Tourney, Big Blind is t400 (9 handed) internettexasholdem.com

SB (t17591)
BB (t13115)
UTG (t3880)
UTG+1 (t19585)
Hero (t9250)
MP2 (t5995)
MP3 (t8887)
CO (t3970)
Button (t17503)

Preflop: Hero is MP1 with K[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/diamond.gif[/img].
<font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises to t1200</font>, <font color="#666666">5 folds</font>, BB calls t800.

Flop: (t2200) 6[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
BB checks, <font color="#CC3333">Hero bets t2150</font>, <font color="#CC3333">BB raises to t6400</font>,