Return trip? Montreal Shanghai Tokyo Shanghai Montreal

Hello,

This may be a stupid question but is the flip side still okay for transit without visa 144 hours? I've seen a lot of examples of continuing on home from your 3rd and final country but not going back to China for connecting flight. If we go Montreal to Shanghai for 2 nights then onward to Tokyo for 7 nights, then back to Shanghai for 1 night, then catch the flight back home to Montreal in the AM. Does this qualify? Its a mirror image of the inital outgoing leg to Japan so I would think so. Is there a minimum time to stay in Japan? Does the transit without visa only work on one voyage?