pinniped

I almost feel silly asking this, but I've never actually flown an int'l-to-int'l PNR connecting in the U.S.

If I fly HYD-DXB-BOS-YYZ, do I need to walk my checked bag through customs at BOS and recheck it? Or does the bag go straight to the BOS-YYZ flight?

I know *I* need to go through immigration and customs, but does the checked bag?

All one EK ticket, with the final flight being a Westjet-operated codeshare.

I've done googling and can't find a definitive answer. Most answers address int'l-to-domestic, which I've done 100+ times and you obviously *do* retrieve your bag and carry it through customs before handing it back to the airline on the other side.