If your horse has a steady and smooth canter, it should be easy for you to follow his mouvement with your upper body. You should try and not move your legs and your hands. It's difficult in the beginning but you'll get it eventually. That will help you be steady. Good luck! :)
Maybe close your eyes and feel your horse, his movements etc. Just relax and follow your horse's movements :)
Sit back. You should feel two butt bones meeting with the saddle. YourRidingSuccess has a good video on riding the canter. Don't pump with your arms .