He's not betting into you, he has position. You have no reads so you don't know if it's a blatant steal attempt or he's actually got a decent hand. Against an unknown, just bet IMO. If they have anything, they'll come along with you.

Checking on the river = bad unless A) you're positive you have nuts and B) you're positive he likes his hand enough to 3-barrel.

You want to get at least 15:1 on your PF call so make sure you get at least that when you do hit your set.