Do I need a visa for China if I will be arriving in Shanghai Sept. 29

then going on to Vietnam Oct. 4 (5 days in Shanghai), then passing through Shanghai again Oct. 29 (5 hours to catch a connecting flight back to Canada). Every time I ask the question I get a different response: yes (two entry), yes (one entry), no (less than 144 hours and connecting flight), yes (a transit G type), yes (your airline - Air Canada - won't let you board without an entry permit) ...