I flew SEA-YVR-HKG-BKK (on CX 713 too!) in December, and they were able to check my bags through. I just told them in Seattle, and in Vancouver they asked for the bag numbers (I would think it depends on AA not Vancouver). I had to clear Canadian customs, although it was pretty easy.
Flying through Toronto shouldn't be too different or too much harder
I guess it depends on whether they are willing to retrieve the bags for you or not.