We've flown Air China 5 times between Vancouver and Changchun via Beijing, and there has never been a problem. Also flew them round-trip between Changchun and Shanghai, with the only negative being a 2-hour delay in departing for Shanghai (attributed to a weather issue for the previous in-coming flight).
Air China seats are nothing special, but not bad. In-flight amenities are pretty standard, the food is edible, and the staff are decent. I can't imagine anyone giving rave reviews, but I also have no complaints.
Baggage allowance between Vancouver and Changchun is a generous 2 x 23kg per person. I initially tried to travel with one bag at around 25kg, but transferred a few things to carry-on at the check-in. Every flight after that first one we've taken advantage of the full load.