Cavalier snoring is very much a breed thing, partly due to the shape of their face. It can also be caused/made worse by the dog being overweight. If it is in good condition there isn't much that can be done I'm afraid. :)
My JD snores so loudly if we stay in a hotel I make sure everyone knows it's him & not me. :D He's spot on for weight & I think it's to do with their elongated soft palate