How do I confirm eligibility?

My itinerary: Canada (home) to Beijing (3 days) to Seoul (4 days) to Shanghai (4 days) to Canada (home). Will this be eligible for the 144 free transit? Note, 2 visits to China within a week but with South Korea in between Beijing and Shanghai.

I am also using multiple airlines so my inbound flight will not show an outbound flight. I can easily print my schedule to show my future plans but is this acceptable? A one way inbound ticket from Seoul to Shanghai? Again, I’ll have a separate outbound ticket availabile to show immigration.

Can I confirm with Immigration ahead of time?