I go for SQ J over AC J any time!
One thing to keep in mind is that clearing US immigration and customs at SFO can be a nightmare at times due to the arrival of many international flights at the same time. That would be the only drawback on the ICN-SFO-YYZ in my view. Not sure if you have a NEXUS card or not, if you do, you can now use the Global Entry, which will eliminate this drawback!