He probably has an overlong soft palate, which is quite common in breeds that have a shorter nose. It is basically just a consequence of his anatomy. The loud snorting that wakes him up actually puts his soft palate back in the right place. It is nothing to worry about and there isn't a cure, although weight loss might help an overweight dog.
We have a cavalier as well, and he snores like an old man. Asked the vet when he had his booster jabs and apparently it is absolutely typical for this breed, nothing to worry about. He snorts when overexcited as well
one of my dogs does this, she is a JR cross and seriously the first time I heard it I thought there was a lorry passing the house lol. I am partially deaf so sometimes I cannot hear certain tones but when I was in bed trying to get to sleep a while ago I could hear this noise and I didn't know what it was. I had to wake DH up and he said 'oh it's Chyna snoring'. I was very She also snorts all the time. She is a little overweight, I didn't know weight loss could help this.