I agree with Trons fairly closely. I think we can eliminate his starting hands as AA, KK, QQ or even JJ. I believe he has a Q and likely either an A or K with it. His play would make sense with 1010, 99, 88, 77 so you would not have to worry about those hands.

Other possibilities are 44 or 22 but I doubt he would have called your PF 5BB raise with those hands. Also I doubt he would have called a PF raise with Q4 or Q2.

As for a flush draw, I do not know many people that checkraise with a flush draw. And also, if he had a set, he would have cold called your flop bet not checkraised.

I think your only scare card is an A (of course not having the third flush card hit would also be good).

I'm betting this hand now to try to take down the pot. If he has a lower pocket pair you don't want one of those showing up on the river.