Just statistics to ponder ...
The argument (or statement) that Asia flights bound for South America, (here, the destination is GRU and the departure point is Tokyo NRT.) are
better through YYZ due to the shorter total distances is only sometimes valid.
The total distances and the differences between them is, in this case, very small. Via YYZ the total distance in miles and km is 11489mi and 18490km.
Via YVR the distance is greater but by a total of 43mi or 69km.
Northeast Asian cities like ICN also show relatively minor distances between the two routes.
From Shanghai and Hong Kong, both considerably further south and to the "east" (or west, if going over the Pacific and not via Greenwich time), however, the YYZ route gets
progressively shorter in comparison with YVR correspondence. If this impacts significantly on fuel costs, then perhaps only NE Asia, Toko or Seoul as a departure point,
could be routed through YVR.
Dreaming, perhaps, but I think rather feasible nonetheless.