Rhythm + Straightness = Distance
Pole work is great for developing your eye for distances without the concern of an actual fence. If you split a pole, not a big deal. For the most part, you shouldn't be dictating when your horse is taking off. You develop the canter before the fence, allow the horse to carry you to the fence, they find their distance, and you just follow them.
Set up a single ground pole and canter a 20m circle over it. Set up pylons or other markers at the other points on your circle to help maintain the shape of the circle. You need this for later exercises. You need a consistent rhythm and pace to be able to consistently get your striding to the pole.
The other exercise is to set up two poles in a straight line 5-6 strides apart. Measure it out. You ride into this in a normal canter until you are confident riding the poles in the target strides. The you try adding one stride, then taking a stride out. Remember, you need to prepare the canter before you get to the pole to get the striding you want.
Tip: if you are chipping the distance, slow down. If you are taking the distance long, speed up. General rule.
Once you are consistently getting the striding to the single pole on a circle, add a pole on the other side of the circle. Same principles apply. Consistent rhythm, pace, line. Count the strides. Should be ~7 strides between the two poles, but depends on your horse's step.
Once you have that down, add the two remaining poles.
It's a difficult exercise, one you can use all the way up the levels. It really tests your ability to sit still, make subtle corrections, and maintain your consistent canter. You can't adjust the canter stride until you first get your 'on pace' canter.
Here's a video of the circle exercise. Yes, its common name is Circle Of Death.
Few things on your video:
Move your hands with his canter. Your hands aren't moving with the natural motion of the head, each stride you are popping his mouth (slack, tight, slight, tight). That's contributing to his high headed carriage. He's guarding his mouth. That'll also effect his rhythm to the fence and your ability to regulate the stride. If you need to, push your hands in the neck. The neck will move your hands with him automatically.
You're pretty decent over the fence itself; flat back, looking up, hands in a good spot. It wouldn't hurt to grab mane over the fences as a precaution, though.
I'd probably raise your stirrups one hole. You need more anchor in your heel, and what kind of shoes are you wearing? Are those flats?!
Nice horse though. He's got a nice natural canter and jump. TB?