If you have decent 'steering' I would say if he 'jumps' into a canter on the trail, just keep him in it, and do all sorts of fig. 8, serpentines, etc...when he is more 'relaxed' at doing that then drop back down to a walk, and try the trot again. Keep doing that until he decides moving into a trot is a better idea. My mare can get pretty "foward" on the trails too, and doing some work that "takes her breath" away, makes her want to chill out and relax and do what I want. She's not so forward as your guy sounds though.
I do agree with working him first in a more controlled environment; atleast then if he does get so excited that he unseats you, he can't get away. There is nothing wrong with working in a safe environment to get the willies out...and I would rather know the horse is calm, and listening to me, before going out, than to go out, and have a terrible ride because the horse is so full of himself he can't help but act like a dork. My mare has been starting out kind of goofy, but I just do a bit of groundwork, and a little riding at home, before heading down the road...works like a charm, and I leave on a calm thinking horse, rather than a hyped up goofy one.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."