I have a cavalier king charles spaniel, who has just recently started sneezing, is this a sign of illness or normal for this breed

Do you mean he's snorting when he gets a bit over-excited? If he's making an odd grunting / wheezing noise as he breathes, you need to put your hand over his nose to make him open his mouth. It's a common thing in the breed. If he's actually sneezing sounds like he might have an allergy of some sort? Why not sign up and join in the chatter, lots of Cav owners here! :-)