...Maybe you should check your trainers credentials!
Let's run the tapes:
Tnavas, my instructor was studying at the Spanish Riding School as well...
...Secondly are you riding Western or English?
If? as you say that your instructor was trained at the Spanish Riding School...
Surprisingly few barrel racers train at the Spanish Riding School, so an English rider is a pretty safe bet.
...Prior to the start of the canter the horse needs to be prepared, by a half halt or two - best done in sitting trot so that you can use your legs with every step...
My gelding was trained on a ranch in Utah, and still refuses to canter on a right lead...but with a bit of verbal encouragement, he'll go from a walk to a canter.
It may be different for dressage, and goodness knows my gelding is NOT an example for dressage riders anywhere, other than what not to do - but it sure seems like it is getting awfully hard to do something basically simple. If you trained a horse to do so, he would enter a canter every time you tapped him on the withers. Right side of the withers = left lead. Left side = right lead. The horse would do it if trained thus. I understand that some cues are more natural than others, and I appreciate the way dressage riders seek to find the most natural, logical way to ask a horse to do something. It is admirable, and a klutz like myself riding a thoroughly poorly trained horse can benefit from the work dressage riders do...but doesn't a lot of it just depend on how the horse was trained?
And in any case, insulting instructors is neither helpful nor friendly, particularly when they are not on board to defend themselves. IMHO.