I think you have answered all of my questions. My wife is a Hong Kong resident and has a 10 year multiple entry visitor visa to U.S, and I believe she does not need visa to visit Canada. So it might be safer for her to hand in the I-94 and get another one on her way in.
Now I don't have to leave a lot of time for the Custom if a connection is needed inside the U.S, but any idea how much time I need to clear the custom at YVR generally?

Thank you very much terenz, I really appreciate it ^