Your horse has alot of potential, he'll be really cute in the hunt circuit. I think you know most of your issues already and you are on the right track w/ a trainer...
I'll hit on the obvious, You know you are a little hunched at your shoulders. You are much too forward in my opinion at the canter. (But hunt riders are forward ...) I think you need to bring your heels down more, your feet are pushed too far forward in your stirrups....You just want to place the ball of your foot on the stirrup. It's pushed way up onto your arch. Now... Scoot forward in the saddle, keep your lower leg back, heels down and roll up onto your pelvis. You are allowing your legs to slide forward while you are attempting to ride in 2 point or jump position but it is throwing you off balance so you are doing alot of bouncing.
I know that sounds bad but you actually arent doing horrible, especially for having had several years off. You mentioned that he's not listening to your leg... It's probalby because your leg is not strong yet. You probably feel like you are giving all of your leg to him, but you probably arent. Just keep working on your seat and balance and the rest will come.
Overall you guys are a really cute pair and I think you will do well together. Good luck!