This may sound silly but when you're cantering count 1,2,3 as fast or slow as you want the canter. The canter is a 3 beat stride and it will help you balance yourself. Also just relax, have decent contact, half halts and circles! The more you practice the better it'll get!
I just do lots of circles keeping my inside rein up and preventing over bend with my outside rein then putting my inside leg on slightly to get him bending around me. This really helped my horse balance himself better
Put 4 poles on a circle. Measure them so they are about 5 bending strides apart (72ft.) Start at a trot and then move to the canter. Ideally, your horse should fit the 5 strides in every time. You can make the poles small jumps to add an extra challenge. This exercise really helps balance a horse who bulges with their outside shoulder. I call this the "circle of doom" because it can be very challenging.