Time to go back to basics. I'd work with a trainer, but for now, stay down at the walk for a little while and improve your brakes. I would keep him in a snaffle.
Basically, an exercise that is pretty hard to screw up when improving brakes is the whoa-sit-reins-back. It works by giving light commands first, then enforcing them as necessary. Like this:
Say whoa. If he doesn't stop, sit your butt down hard. Still not stopping? Grab his face and scoot him backwards. Eventually he learns to stop on "whoa" before you even get to his face.
Do this at the walk until he stops quickly. Then try the trot. Then once you guys get it own pat, go ahead and do it at the canter. Be prepared when you go up to higher speeds for it to get sticky again. Sometimes you just gotta fight it out (For lack of a better term)
But seriously, if you're scared of hurting him by pulling, don't be. If he's not stopping he is a danger to you and himself. If you really are hurting him, you'll only have to do it once before he gets the message. Not really fun, ideally he will stop with lighter signals, but if the horse has these problems you'll have to go there a bunch and eventually he'll soften up and realize what you are asking. I'm not saying to bloody his mouth, but definitely give him a "HEY! I'm still UP HERE!" talkin' to. And immediately release when he takes two or three steps back and make him stand, don't go off right away.
It's pretty amazing how fast horses pick up on stopping from this.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.