Per this thread in Flyertalk, Air Canada is offering returns between Hong Kong and San Francisco via Vancouver for as little as C$500 (HK$3,080). The same price also works to LA. There is good availability in January and February. The flights go through Vancouver. It seems that you cannot have a stopover (24 hours or more) there at this price,
We’re talking about roundtrip flights from all around Western Canada on Delta Airlines to Shanghai Pudong PVG and Beijing PEK, China for about $500-$600 CAD all-inclusive of taxes and fees. That’s absurd! The Shanghai flights are closer to $500 and Beijing flights closer to $600 CAD.