I tend to cinch up very slowly, always. Will he buck/pull back/jump up if he is tied? If I get a cinchy horse I spend a lot of time rubbing them with the cinch and letting it fall, tightening some and letting it fall again, etc. The important thing is to only pull the cinch until he shows signs of discomfort, then hold it there. Once he relaxes, loosen the cinch again and rub him. He will learn the pressure only goes away once he is relaxed and accepting, and will also teach him that just because he is cinched does not mean he will feel pain.
Do some groundwork with him when you do get ready to ride. If he bucks, get after him like a crazy person. I mean, do anything except let him do it. Disengage and chase his hindquarters, run him backwards or sideways, chase him with the whip, anything. Only stop when he wants to move forward nicely.
This same thing applies to riding. If he starts bucking, do a one rein stop (Pull his head to your knee on one side only) and kick him in the hip to make it move. That will take away his forward motion. Be sure to be aggressive about it. I mean, really make him go in a circle. Then take your leg away, let him stop, and ask him to continue onward again. He'll learn doing as you ask is a lot easier than bucking or humping up with you.
If you feel you cannot sit the bucks, jump off if you can and get after him.. Same thing. Run backwards, sideways, chase his hip in a circle, anything you can. Make him think you're going to eat him. Be scary. Then just forget it happened, get back on, and continue calmly.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.