Going into a jump at a certain point the horse will loose sight of the fence. He may not understand when to pick himself up hence the 'running through the fence'. You need to be his eyes, you need to guide him and let him know when to take off.
The being more forward in canter comes from your body and his response to you. You need to work on transitions, walk to trot, halt to trot, walk to canter, trot to halt, halt to canter etc. That will build him up behind and give him the go needed.
Pole work to see strides helps too. Rather than just jumping, put poles on the floor and a stride from the pole ask for canter. Make the transistion further away until he's looking for it with you. Then, you need to add a small fence and build it up.
The flat work needs to be right to be able to jump correctly. I hope this helps.