They did operate YVR-TPE for a few years. Cancelled at some point, anywhere between 5 and 10 years ago. Then codeshared on BR YVR-TPE. Then when BR opened the route YYZ-TPE, they cancelled the codeshare agreement.

I would not expect AC to restart any time soon. I would imagine AC is still upset that BR is flying to YYZ. No codeshare at all between them, either of BR on Canadian domestic routes, or of AC on BR Asia routes.

You want to buy YYC-YVR-TPE, only way is through a TA. Not on aircanada.com, not on the BR site either.