I don't believe any horse is fully one breed if, within 4 generations, there is another breed.
My question is, is this (stunning) stallion a perch x appy cross, or is he out of two sugar bush horses? Because if he's a perch/ appy cross, he's a cross, like greysorrel says. If his parents are both sugar bushes, as in, they're NOT just a perch x appy cross, and the only perch/ appy cross is way back in his pedigree, then he's definitely a sugar bush, and it's a breed.
But breeding nonsense aside... WOW. GORGEOUS. HORSE. If you want to keep sharing pictures... I won't stop you, lol. Whatever he is, it doesn't matter to me when he looks like that.