I'd suggest there's a slight difference in meaning and intonation. In "I'll leave it to you" one might want to say, that they are going to leave something for you to do, so they aren't going to so something, but rather leave it to you. Also, in this sentence, "to" is stressed, so it sounds "I'll leave it TO you"

"I'll leave it for you" might mean a person is leaving an actual object for you, like a piece of cake.

They are both correct. There is a minor difference in tone that even I can't remember what it is.