he IS a nice horse. it's no wonder you like him.
I kind of agree with Waresbear. I think you are riding his mouth a bit much. I mean, you have quite a bit of contact, to which he sometimes seems to be a bit braced against. maybe he is getting that way becuase he does not get enough of a noticeable release when he DOES give to contact.
you do much better at the walk and gait than canter and your position is not as bad as you make it out to be. But, at the canter, you get a bit braced in the body, which is what cuases your arms to want to flap. the motion has to be absorbed in the hips, or it will come out the upper body, and flapping arms is a prime result of that. thing is, when you are flapping, it means the bit contact will be uneven, too. it looks like he gets excited at the canter, but even so, let him have a release from the bit once he earns it. So, if he is ignoring the bit, get strong enough that he doesn't ignore it, then release bigtime. not inbetween contact the whole time.
you have done well with this horse and show potential to be a very nice rider.