Three Bet this River?

[Vern]

Table is refreshingly loose for stars, working off some bonuses finally with the looseness.

MP2 is a loose passive preflop and aggressive post flop when he hits.
UTG+2 is seeing about every flop and open-bets anytime it is checked to him on the flop.

PokerStars 0.50/1.00 Hold'em (10 handed)
Props to Bison for his converter

Preflop: Hero is MP1 with A[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/diamond.gif[/img].
UTG calls, <font color="#666666">1 fold</font>, UTG+2 calls, <font color="#CC3333">Hero raises</font>, <font color="#CC3333">MP2 3-bets</font>, <font color="#666666">5 folds</font>, UTG calls, UTG+2 calls, <font color="#CC3333">Hero caps</font>, MP2 calls, UTG calls, UTG+2 calls.

Flop: (19.50 SB) 4[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/heart.gif[/img], 3[img]/images/graemlins/spade.gif[/img] <font color="blue">(4 players)</font>
UTG checks, <font color="#CC3333">UTG+2 bets</font>, <font color="#CC3333">Hero raises</font>, MP2 calls, UTG folds, UTG+2 calls.

Turn: (12.75 BB) Q[img]/images/graemlins/heart.gif[/img] <font color="blue">(3 players)</font>
UTG+2 checks, <font color="#CC3333">Hero bets</font>, MP2 calls, UTG+2 calls.

River: (15.75 BB) 7[img]/images/graemlins/diamond.gif[/img] <font color="blue">(3 players)</font>
UTG+2 checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP2 raises</font>, UTG+2 folds, Hero ???

What do I do, he plays loose/passive pre-flop but steps it up post flop. I don't see anything the river brought to help him and it is now heads up. Do I three-bet this or call? Thanks