Cantering

So when I ask my horse to canter he can get quite fussy. He refuses to pick up his right lead and has even tried to buck. I have tried circle, shoulder ins/outs etc everything. He just had his teeth floated and this is under several different saddles. Anyone know what I can do?

Are you going into the canter from a nice, balanced trot? ;) Remember to slide your outside leg behind the girth, & press your leg against the side.

But having a nice balanced, relaxed trot really helps.

Nice, easy balanced trot-yes.

Anyone else?

How old is the horse? How long has he been in training?

He is 6, was not properly trained as a youngster. I haven't been consistent with him either which hasn't helped. I believe they taught him to fall into it. Meaning trot so fast until he feels like he will fall and picks up a canter. His left lead is so strung out, and messy

My horse used to do this and i've had many others as well, what I would do is wait till we would get to a corner at a nice rounded trot and very slow so he's really sitting on his hind end and then ask for the canter but lift ur inside right hand up about two inches so it forces him to lean back more. This will help him to be more balanced and his head will be up so that he cannot buck and really get him to understand that you want him to pick up the right lead. Eventually you can use this technique on straighaways and then you wont even need to lift ur hand after more practice.

Does he canter on his own out in a field or on a lunge line?

Put him on the lunge and teach him that way.
If you are doing even the smallest thing wrong, you could be disrupting him. He needs to learn on a lunge line with side reins a voice aid to canter and get his own legs in order, and then use the voice aid under saddle to re-enforce your leg aid for canter.
Also as previously said, while giving the aid make sure you are not inadvertently leaning forward or pulling, only putting your leg back.

I ask my horse to canter the other way. I put my inside leg back, and the outside leg forward. That way I'm "blocking" the leg that I don't want to lead, and freeing up the leg that I want him to lead.
Also I motion with my body and arms how I want him to start the canter. I look stupid doing it...but it works really well.

Has he seen a chiropractor? Not picking up a lead could me that he is out of adjustment.

Does he canter in the pasture? Does he pick up both leads out there?