Trying to train for dressage, I started cueing with the dressage cue from the start, inside leg at the girth, outside leg slightly behind the girth, slight bend to the inside while holding the outside rein in contact, not pulling but just supporting, and seatbone shift also to the outside to lighten and lift the inside shoulder, though he isn't heavy on his shoulder now.
Yep, that's how I was taught and how my horse best responds.
I "play" (another word LOL) with the inside rein and support the outside rein. By play, it's merely preventing him from bracing against the bit or the reins, but encouraging him to stretch and keep going without throwing his head. It's similar to "vibrating" a rein.
Bend to me is the same thing as what mildot described, wrapping the horse's spine around the inside leg, poll to tail. Flexion to me is bending at the poll (not the neck, unless you're asking for that specifically as a stretch.)
But how I cue my horse. I put more weight down the inside leg, slightly sit on my outside seat bone, make sure my outside rein is supportive which means by my side as close to 90 degrees as I can without bracing or being stiff, my inside rein is supple but there is still some contact, I move my inside leg on the girth, my outside leg slightly behind the girth, half halt to prepare him, squeeze the inside leg while holding the outside leg in position, and tell him 'canter'. He's green, I'm new.. but that's what I was taught.