what do you mean look to your self for leadership, what should I do? When he stops I tell him to keep going by using pressure and clicking and kissing but nothing
what I meant is do not look to him having some kind of issue with cantering under saddle, since he will do this elsewhere. It's not HIS problem, it's yours. I don't mean to sound harsh. Only, that when you look to yourself for the answer, you will be ready to learn how to change this.
Clucking and kissing are obviously not enough. You may need to smack him one, with a crop/whip or the long end of the rein. Get him to leap forward, then let him just coast along a bit. Dont' stop him as soon as he leaps forward, but don't drive him non-stop either. Put your leg on him and kiss, then one more leg, stronger, then wallop him! And be ready for him to jump forward, so don';t jab him in the mouth or haul him back when he does, but let him coast forward and tell him he's a good boy (he went forward!)
Fundamentally, the horse (who is a gorgeous animal and looks capable of handing a long canter with ease), does not think you are capable of making him move when he thinks otherwise. This is what the fundamentals of leadership are; getting you horse to move when you say so.
Did I miss where you said you had anyone helping you? With some instruction?