Vida, that's an interesting question I just discussed today with my trainer. In fact cues can be different depending on horse. The standard one is you establish a nice forward trot with bend on circle and then ask for canter with your leg/seat (inside leg is asking, outside stays behind the girth).
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."