My internet is being mean so I can't watch the video. However, I think some insight can still be provided.
We don't "work" on collection, first of all. Collection is the sum of all parts, what happens when all the puzzle pieces are in their correct place, when the picture is complete, etc.. So obviously something is not in the right place in the canter here.
The first thing which I tend to accuse is the line. The line can be excused in the walk and trot on most horses and they will go along fine, but because the canter is an asymmetrical gait, the line is of great importance. We must always ride on our line, not the horse's line. We ride the forehand as a whole on this line, and the hind legs follow. When the horse is in balance and rhythm, maintaining our line is easy. When they are not - it is hard. This is the first thing that you should begin to chip away at - riding perfect figures perfectly in all three gaits.
After we expect order laterally, we can begin to expect it longitudinally as well. This is the most basic step on the training scale - rhythm. The horse must be metronomic - your first stride must dictate the rhythm of all the strides of the gait. To fix this in any gait with a horse that speeds up - naturally we must slow it down. (And conversely with a horse who slows down - we must speed them up). With some horses this is not an easy feat either because of their temperaments or their conformation. The most basic correction to slow them down is obviously to simply come down a gait, re organize and try again. If that doesn't work (in your case the trot is still fast) we would go down another gait (so to walk) reorganize and then trot and try the transition again. Rinse and repeat.
But remember, perfect practice makes perfect. The line must remain in order to keep the lateral balance and support the longitudinal balance. Your position must also not change in between gaits. No leaning forward, back or side to side. Simply an application of the leg and seat aids. The hands do not move either.
As you are able to control the rhythm through transitions, and the horse becomes relaxed and accept the contact in a round frame, we can begin to delve a bit deeper. This is where transitions in the gait (here we'll call them balancing half halts, or just HH) become important. Now it is important for the horse to begin to get a basic understanding of what the HH means. When the horse begins to lose balance and rhythm, apply a HH to re balance the gait. If this fails - educate by doing a transition down a gait and trying again (as was done before). This serves to correct the horse. As this is repeated then he will begin to learn what a HH is and how to respond to your aids in a positive way.
They say money doesn't buy happiness -- well happiness doesn't buy horses!