Flights with connection -Same airlines

Hello,
I'm a Canadian passport holder and I would like to flight from Japan - China (Xian) - Canada. I have two questions concerning the visa:
1) The flight from Japan to China (Xian) is with Tianjin Airlines but it's not direct flight, there is a few hours of connexion in Tianjin. Is the 72-hour or 144-hour free transit applicable?
2) If so, should I apply for it at Tianjin Airport or Xian Airport?
Thank you very much in advance.