after calling preflop, it is free to get to the turn. He could very easily have the straight or flush draws so bet the turn HARD.
I dont think slowplaying the flop is too bad here (although i personally would bet as i bet preflop) if he called with 33/ 99 / AJsorta /hands he thinks hes winning and you want to build the pot now as well as the whole bad odds to draws thing.
If he called with another PP or someother hand then he probably isnt going to give you any more money anyway so dont be scared to bet and see him fold