If you don’t have the luxury of a ménage ‘insides and outsides’ can get confusing. Your inside is the direction you are turning so if you turn left at the corner or end of the field then left is your inside. The outside is therefore the other one!
In canter your horse strikes off with the outside hind – hence your outside leg comes back to tell him which leg you want. The inside hind and outside fore go together. Last is the inside fore which is called the leading leg. This is the leg which your horse puts out to balance himself, similar to you putting your hand out to stop yourself falling. The more weight you can put onto his hocks the more balanced he'll feel and the less he'll need to lean on that shoulder.
Help your horse by sitting back and looking up as you ask for canter. Riders often lean forward and to the inside because they think it will encourage their horse to canter. All it actually does is put more weight over the leading leg putting the horse onto his forehand. This makes the canter flat and the horse fall in.
Trot to canter transitions create more problems than any other. Treat it as you would treat a walk to trot transition. The less you make of it the calmer you horse will be.