If you have 33 preflop and are called by 1 person, he will almost always have overs (the only way he wouldn't is if he held onto 22 or 33)

In tournaments this is called a race and it happens often in the later stages. 1 person will go all-in with a pocket pair. Another will call with 2 overs. It's approx a 50/50 for either hand to win... When you take it to the river. The pair is usually a sligh favorite. But it depends on the hands.

In a ring game you will rarely see this type of hand go all in pre-flop. So you have to play every street individually. I still play my streets on a 50/50 basis. Either he hit a pair or not. You just have to look at betting, player style and opportunity to determine. But 33 isn't too strong unless you trip it.