If the problem isn't oral, heres some advice =)
When my horse would get "explode-y" I would concentrate my energy on bending, circling, flexing, and weaving. The Arena I ride in has tons of jumps in it. I would constantly weave in and out of jumps, circle, leg yield, move from a 20 meter circle to a 10 meter circle.. figure 8 at the trot, etc. If you don't have jumps, get cones (sold at Lowes or Home Depot) set them up randomly all over your riding space and just weave from pole to pole. This will get him listening to you, since he doesnt know which way he is going to turn next.
The canter can be very hard to control once they blow. Once my gelding 'sploded.. it would take me more time to get him back, haha!
I would recommend setting a goal with each ride to attain a more controlled horse. Your goal.. get him to walk at the pace YOU are comfortable with. This could take allot of trot work.. or not much at all. Once he walks at your pace, continue the ride for about 10 minutes at first (expand this time period with each ride) then dismount, untack, and praise! Cookies, Carrots, whatever! When he realizes that he will be rewarded with being untacked and spoiled when he chills out.. he will begin to do it on his own =)
This will take time and consistancy! Dont get too ahead of yourself!
By the way, he is HANDSOME!