Those are nice!! Are they the Pessoa's?
They honestly look a tad big.. I'd worry about that much excess and on such a high hole already.. Leather will stretch with use, so you're kind of stuck, if the straps stretch at all. They might could slide down a little lower on the leg. Just a little.
Your horse looks like he has tall, thin legs. That can be hard to fit at times. If you went a size down, then they might be too short to cover the cannon properly, but in the meantime better in width for covering the leg...
"You're just as sane as I am."~Luna Lovegood.