Nikki,
Ponies. Driving ponies.... A blast, but a little bit of work. About the short strides first. In order to get him to have longer, more relaxed strides, you're going to have to school a bit. Lunge quite a bit, (not too much though so he gets bored) and work on voice commands. Especially canter. When you ride, exercise yourself as well, and slow things down. How slow can you make your horse trot? After you have a mastered slow trot, your horse will calm down and relax. Then you can start asking for some lengthinings in stride. The trot will be faster, but shouldn't be "rushed". Then, bring back to slow trot, and make your canter cues clear, concise , and sharp. He should never, under no circumstances "rush" or "run" into the canter. You're better off doing slow relaxed transitions then rushed ones just to get the canter over with. It might take time for the canter, but it's worth it. I also reccommend LOTS of walk/trot , trot/walk and other transitions. I can't even count how many I've done in my life, but I can tell you that they are in the top 3 most successfull exercises that I've done. Eventually when you are ready, walk to canter, and even canter to halt transitions are great. Another great one is 4 stride switches. I believe that this should be done ALWAYS IN A RING. While on a circle if your're uncomfortable around the whole ring. Start at a point and halt. From halt, move into walk for ONLY four strides. Then halt for a few seconds. Repeat around whole circle until your horse starts relying almost 100% on your weight shifting back and to the point that you're barely asking for a halt through the reins. Next halt again, and move into the trot for four strides, then walk four. Trot four, walk four. You can do this with halts for a few seconds, or walk a few strides. Your horse's canter will naturally slow down and he'll be waiting for your cue to learn what to do next.Remember, to not overdo any drills and don't get frustrated. Your horse might learn slowly, but a solid foundation is better than a weak one. Remember while doing these that you should try to get your horse to respond to you weight and seat moving back rather than you pulling. Good luck! Hope this helps