Am I eligible for the 72 hour visa free transit?

I have a roundtrip flight (Winnipeg, Canada-Shanghai-Winnipeg). I fly from Winnipeg to New Zealand on Dec 11/2015, transiting from Shanghai (PVG). I'm only staying in the airport. However, on March 1/2016, coming from Vietnam, I will be going to Shanghai and want to stay less than 72 hours to see the city, and take my flight back home to Winnipeg on March 4.