After seeing the video there were a few things I noticed, first being the transition from the trot to canter, it seemed rushed and as though he fell up into it- that bad start alone will cause problems for you later in your canter work as now you already have one thing to fix in the gait. If that happened I would bring the horse back down and try it again, making sure to check and not let him rush the trot and run up into it.
As for what I was mentioning before about up/down striding, you seem to do a bit of a mix. As Clava mentioned, you have quite an active seat, but, (and I think I heard your instructor mention this as you were riding) if you thing of sitting deeper, then riding Up on his up stride, you may get a slightly more upright canter out of him.
Your legs seem to be pretty active- is this due to trying to keep your balance or is it for keeping him active/ awake?
Overall I can tell you both are working very hard at what you do- so keep it up! :)
We are not human beings having a spiritual experience. We are spiritual beings having a human experience. -Pierre Teilhard de Chardin