Why is it more difficult to stay with a horse when jumping up a bank? It's because they have to jump much higher to be able to put their landing gear down at the top of the jumping arc. You need a very specific type of canter on the approach to an upbank to produce a good jump. Learn about it here!
"If the rider encounters a problem, he must first look for the cause in himself. Most of the time, the rider is the cause of the problem. Only someone who looks at his own riding critically and is willing to improve constantly and learn more will be a good
Your balance and the strength of your core are what allow your position to be unaffected by your horse's changes of speed.
"The quality of a good canter: round, energetic, straight, cadenced, light. You have to feel in the strike off that the horse lifts his forehand without throwing himself forward." ~ Nuno Oliveira
To keep your horse straight in the canter, always be thinking of a slight shoulder fore positioning.