Seems like march 1st, AA & DL put this YYZ-PVG back on sale. Not quite as cheap but still better than it was just 24hrs ago.
AA has $2092usd pretty much any Tues-Thurs departure from May-Sept, on the 787 YYZ-ORD-PVG route.
DL has less selection but they are also at $2092usd on mostly Mon-Wed departures going YYZ-MSP-SEA-PVG with 767 lieflat.