What position did he open from pre?
I don't like flatting pre unless the opener is a nit who instafolds KK to any raise and I don't like flatting any player type if they opened the CO or BTN.
The x/r on the flop is crazy strong, so when he calls it, look out! He's telling you he has garbage two-pair beat or he's a calling station with any draw. After flatting pre, I like a donk lead on that flop much more and again, if he calls it, proceed with caution.
On the turn, what would you do if you were on a draw? Filled up? Made trips? What's a reasonable hand to rep for flat pre, x/r flop, paired turn that makes a flush? Particularly after he calls the flop? 180ish in the pot with 310 behind, I dunno, any line pretty much sucks. I guess I lead 100 and if he calls, shove the river, but I'm not happy about it.
Compare to raise pre to 50, he calls, 100 in the pot with 300 behind on the flop, I lead 75, he calls (if he raises anything more than min, I probably dump out -- depends on how bluffy he is, but live 1/2 I tend to give credit to post-flop raises on a flop like that). Now there's 250 in the pot with 225 behind. I probably check there and see what he does. Most live players will check their whole range back there, particularly boats, or maybe bet silly small if they have the nuts. I probably check any river, since a lead basically turns my hand into a bluff. On that board, I probably fold to any bet over 100, unless this guy gets bluffy on the river. Without the made flush, I might call more often, but I probably still don't call a shove.