I don't believe in horses starting with the wrong lead just to get off the work. First, because wrong lead on circle is not comfortable for the horse, second, because the transition lope -> trot -> lope takes more work on horse's side then just loping around. Also if horse is stiffer on particular side (and it's always or at least almost always a case) it may be more difficult to pick the correct lead.
Personally I'd establish a nice forward trot (NOT rushing) on 20 m circle with slight bent to inside, and when you feel you are balanced and ready yourself ask for the canter (inner leg at the girth, outer leg slightly behind the girth, slide your hips).
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