Looking at the hand, even though you are drawing, there are only 5 holdings to which you are a dog that he could be playing. If he has JJ, TT, 55 you are 34% to win. If MP3 is holding AA you are 46% to win. Finally if MP3 has JT you're 45% to win. Against all other holdings you are a slight (any pair 52-56%) to dominating (any draw) favorite. (
TwoDimes for the calculations)
This leaves the questions of what hands could he limp-call pre-flop and then lead 300 into a 405 pot on this flop and whether or not he can call a raise of 680 for most of his stack with that hand. Clearly you are not looking for a call here as the best you can hope for is a coin flip and being the better player (2+2 assumption) you want to avoid coin flips. Not knowing the player my read on this player before his call is AJ, TT, or KQ as the big pairs (AA, KK, QQ, JJ) are likely have raised the limpers and you have the Ax flush draw. In low limit SnGs I've seen all sorts of hands turned over in the early rounds so who knows what the correct read should be. In the end the limp-call-lead gives me pause. Players rarely do this with nothing. I'd wait for a better opportunity even though you may be a slight +EV. You have position on this guy and if he thinks you will roll over to a flop bet he'll try it again later when you'll have a better holding.