Breed just has nothing to do with training. You can't ride papers. It should make no difference what the breed of horse, or if he is registered, rather the relationship the rider has with the animal.
I ride a 14.3 HH Canadian. He moves a bit different in the front end than most horses out there and is quite a stout animal. No one would think English disipline when looking at him. I placed quite well in english flat classes, equitation classes, hack classes, and at the end of the year I had him jumping 3'! Not what most would expect from a short heavy horse. He does quite well in the western pleasure stuff, the reining classes, trail, barrels, etc. I have started him under harness for driving classes. We have a very good horse/handler relationship and the training follows that. I am now working on some trick stuff with him. I want to have him bow on command while I'm mounted. It's coming along fairly well.
Any breed of horse can do anything. Some are just the 'norm' for that disipline and some are a surprise. I think it makes for a more interesting class to watch. If they are all the same breed and shape, things get a bit boring when you are a spectator for sure.
Papers can't be ridden and a good horse has no color.