One of the things I noticed early on in my riding career was that if I had problems getting the canter I magically knew it before hand at the walk. Using that ah-ha, I started paying more attention to my horse's walk asking myself, "if I want to canter right now, could I do it?" Through trail, error, and success I developed a feel for a walk that was sufficiently balanced for the horse to produce an obedient transition into canter. Problem solved...so I thought.
Then I started paying attention to the canter--mostly after seeing other people doing lovely canters on their horses and beating me at horse shows. With a better picture in my mind of what I was trying to achieve, I set to work to improve my horse's canter. This wasn't easy. Rocketing around the arena is not as conducive to thinking and analyzing as is the more sedate pace of the walk. Repeated efforts brought little improvement. Besides, it's freaking scary.
To preserve my life, I decided to shorten the duration of each foray into canter. Better--but not great. I shortened the duration further, with some slight improvement. Then I noticed the transition itself. If my horse tossed his head up for the transition, the canter and subsequent downward transition to walk was mediocre at best. Instead, if he raised his shoulders in the transition the canter was soft and lovely and the downward transition effortless. The solution was to have my horse raise his shoulders in the transition...but how could I make it consistent? I tried to keep his head down, hoping the shoulder would rise. Are you surprised things got worse? I didn't think so.
One day I happened to be reading a reference to a German philosopher by the name of Georg Wilhelm Friedrich Hegel (1770-1831). Besides being touted as the last man on earth to know everything (I seriously doubt that particular boast), and quoted as saying something like, the lesson of history is that man learns nothing from history (what a card), he (reportedly) said something I found useful. Paraphrased, for my use, it goes something like: You can't achieve a goal by doing the goal. I ruminated on this for a bit. Could it be I was trying to fix my horse's canter with the wrong approach? Next time I saddled up, I brought along my powers of observation. Within my fumbling around I noticed my horse's balance, straightness, and acknowledgement of each of my aids. When I addressed each of these items at the walk, and saw that my horse understood what I expected, the canter transformed.
Hegel was right. You CAN fix the canter by improving the walk.