hidden opportunity?

[willie24]

AP 15k rebuy ($30), rebuy period is over. about 100 left, 27 paid.

relevant stacks:
hero 5400
mp2 4135
mp3 11780

big blind= t200. no antes.

hero open raises to 600 in utg+1 with 6 [img]/images/graemlins/spade.gif[/img] 6 [img]/images/graemlins/diamond.gif[/img]
called by mp2 and mp3. all others fold.

relevant reads: mp2 has been pushing some limped/unraised pots. seems to have an understanding of fold equity in combo with pot odds. looks like pp to me, but not sure.
mp3 has been playing "big stack" poker. could be pocket pair. could be big ace. could be prospecting for pussies.

flop (2100): A [img]/images/graemlins/diamond.gif[/img] J [img]/images/graemlins/diamond.gif[/img] 2 [img]/images/graemlins/diamond.gif[/img]

hero checks, planning to fold. check, check.
hero now suspects mp2 is willing to give up. mp3 is a question mark.

turn (2100): 4 [img]/images/graemlins/spade.gif[/img]

hero bets 1200. mp2 folds, mp3 calls.

river (4500): 5 [img]/images/graemlins/heart.gif[/img]

hero checks planning to fold, as every pp beats him, (in addition to anything better)

but...mp3 pushes. hero has 3600 remaining.
thoughts?