[Domer]

Stack sizes would be really helpful for this one. Lets say that half of the time he's got top two pair, half the time he has a set of 3s or 4s. A set would mean that you have 9 outs (ignoring the possibility of a boat), and top two would mean that you have 12 outs. With two cards to come those leave your odds of winning at almost exactly 35% and 45%, respectively. (You can find these numbers in almost any poker book.) This averages to a 40% chance of winning if you play the hand to the end. (Obviously if youre sure he has Q4, then your chances of winning are 45%.)

With exact stack sizes, we could probably break it down even further, taking into account how often a raise will make your opponent fold and whether that offsets the fact that you're an underdog in the hand. With no other information, I would lean towards a small raise here in the hopes of a free card on the turn.