Originally Posted by
DavidDTW
DL should check your bags thru to PVG, but you will have to clear customs and go thru security again. So you will have to collect and recheck your luggage in Toronto.
I'm not certain this is accurate. Both DL and MU are in T3 according to YYZ's website, and multiple threads
(1) (2) state that USA-INTL can stay airside.
To answer the OP's other question, regarding checked bags, yes, DL will check all the way through. Whether one ticket or two, MU is a tier one Delta partner and on the list. They may need to ask the agent to check the list, but they can do it.