As 67s is probably the worst hand you open from EP you definitely shouldn't defend against a 3bet from the button, I would sometimes defend this hand if I have position postflop(depends on the opponents 3bet % too).
Check calling the flop is ok because you have enough outs but I would probably check raise to something like $2.5 . Reason for that is so you fold out his overcards like AK, AQ, AJ and KQ that don't also have a flush draw. The reason I don't like check calling so much is because you too often find yourself in a weird situation like this one. I'd probably raise flop and get it in on the turn to get as much fold equity as possible. But the main problem in this hand is that you defend against a 3bet too wide and get in sticky situations like this, even when you flop great you still aren't too sure what you are supposed to do. Some better players could tell you something different but that's my view on it. Hope it helps.
