My first horse was a TB who was exactly the same. I rode with a long schooling whip. In the walk, if he wasn't off my leg a quick flick-flick (not hard, just taptap) behind the leg to wake him up. Repeat a few times, and as necessary. Usually after 2 or 3 taps they get the idea and work off your leg. At times throughout your session you may need to revert to the flick-flick again, should just take 1 reminder though.

The only other thing with the canter is to ensure you are sitting balanced, evenly, and keeping a good supporting contact.