@JB you and I are in complete agreement. If you read all of my comments, I suggest the same over poles only.
I would love to see a video of OP doing lines in striding asked for to a standard A hunter line on aforementioned horse. A horse already short at the standard distance will really struggle to leave it out in practice, especially over poles where there is even LESS distance on the backside covered by the horse. Especially one that appears unbalanced/ lazy enough to break to a trot while coursing?
I rode 3rd Level + I am very aware how to gain adjustability. Upcoming show for OP, should do the add step until they can consistently nail the set distance from the appropriate track and rhythm at home. A competent trainer would also teach inside leg to outside rein and this wouldnāt be news to a showing client and OP likely wouldnāt need to be asking the internet how to gain power at the canter.
I donāt even know how you learn to canter without inside leg - outside rein? Literally step 2 here: https://howtodressage.com/troubleshooting/canter-correct-leg-lead/
Again, not everyone who has horses has trainers, but if youāre actively showing hunters at an A show and wanting to place ā a good start would be fully riding inside leg to outside rein under trainer supervision OR post videos and photos so people can accurately diagnose as best they can over the interwebs.
Hopefully the OP gets video and the show and we can see what comes of all this! I notice only a few people willing to post photos and videos of themselves to describe what theyāre looking for advice on. Iām always willing to put myself out there!
Iāll see myself back to the eventing and dressage boards & only chime in non-hunter advice. I recommend a few dressage lessons and a spin the jumper ring to the OP.