I know this is probably a basic question, but how does Marriott decide what type of room to give you when you redeem points for a stay?

I am looking at a trip to stay at the Niagra Falls Fallsview hotel, cost shows to be 60k points. There are about 15 different categories of rooms, so I wonder what am I likely to receive? Is it based on a formula, reward level, or availability? I am a silver, would it different if was gold/plat?