There is an obvious answer: China and Canada have negotiated a favored-country tourism status agreement that allows Chinese tourists to travel on a regular tourist visa. This is a status China has granted to many other countries. However, because the Harper government has an axe to grind with China, and is bent on playing silly ... games with it, the Chinese haven't implemented the agreement. So the market in China for visiting Canada is severely constrained. When that agreement is implemented, it will mean more business for both Canadian and Chinese carriers, and larger aircraft. It will make more sense to spend promotional dollars in China. Right now, why do a major PR campaign when most of the population cannot visit Canada? Three weeks ago Milton said AC is considering a fourth Chinese destination for next year (Guangzhou). But he wouldn't commit to it. The only reason I would think is the lack of the tourism agreement. If the tourism agreement comes into effect, AC will promote Canada, AC will add flights and AC will put 777-300ERs on some routes. This issue has nothing to do with AC, the age of AC aircraft, or even price. It's all about Canada-Chinese relations.

This recent article sums up things pretty nicely

http://travelvideo.tv/news/more.php?id=10145_0_1_10_M