The canter is an important pace for a competition horse, regardless of the discipline. It needs to be adjustable and enough quality to enable them to perform well – whether that be jumping or in the dressage boards.
Once your horse is going forward into an even rein contact, you can start to think about varying the pace (or riding the gears) in the canter work. To start, ask for a couple of strides of a more forward canter, and then back to your horses normal canter. As you bring the horse back, you can encourage the self carriage by keeping your leg on and offering the rein forward to teach them to carry themselves. Once your horse becomes more established with the idea bring the canter back slightly from the working canter, then forwards into a more medium canter stride and back to working to develop the elasticity of the pace.
Its really important to keep the leg on so the hind leg keeps coming forwards and the horse doesn’t fall onto its nose – you are aiming for being able to ride between a bigger and smaller canter stride off your seat rather than relying on too much leg or rein aid.
Building on this, improve the quality of the canter by leg yielding out on a circle into medium canter. Using your outside rein and leg to guide the horse back to the smaller circle, without asking the horse to collect again (let the small circle do that for you!). This encourages the hind leg to keep stepping round and under which will improve the connection of the work and you should see this reflected in the marks for your canter work.