yep, Sonny does that ALLLLLL the time in a canter...you can't prevent him from doing it.
Does your horse love to canter? Sonny's problem is that he absolutely LOVES to canter so he gets overly excited, which is causing the "huffing" during the canter.
It's also a TB thing...most TBs, I've noticed snort while cantering, and since most Paints have TB blood in, that also explains why Sonny is snorting.
It's nothing to worry about...we mentioned that to the vet when I had the pre-purcahse done and she said it was normal for some horses