Nope. They are not allowed if they hold a China Passport. They won't be able to board the flight at China for flights to Taiwan. It has nothing to do with the Taiwan immigration or customs.

The cabatoge mentioned are correct, though, so one cannot compare YVR-JFK v.v. or YVR-IAH v.v. to SEA-IAH v.v. or ANC-EWR/JFK v.v.

Let's hope and dream that CI introduces TPE-YVR v.v. to 2x daily and tag flights to JFK and IAH using smaller aircrafts such as 343 or 738

For BR I doubt YYZ will be increased to daily before New York. 5 weekly sounds about right.