100nl straight vs unknown

[kabouter]

Ah I wasn't sure here, since it looks like he is on a straight/flush draw, wouldn't checking the river be better? I mean this was the first orbit he sat at my table so besides the fact that he called my pot sized raise on the flop and turn (pretty quickly). I have no reads on him.

Sure he called here, but what do we expect to call my river bet here? A2? A4? 2pair/sets? Kx?