How can we answer this question without knowing anything about the guy or knowing what action was preflop?

You need to assess what range of hands he may be holding. Unless you put him on a strong ace or a deuce (unlikely) the pot is there for the taking and even if you're beat now you have plenty of outs.

A raise will define your hand but if he comes back over the top you will have to fold so I think calling is the better option.

To be honest though why are you in the hand in the first place? As far as suited connectors go 34s is pretty dire and I doubt that you had the implied odds to play the hand in this situation. If you're going to play the hand, this was a perfect flop for you so I think folding on the flop would be a terrible play.