Ms Helper,
Thank you.
What would happen if I were refused to pass the customs?

In principal, you can't use the Home-Visiting Certificate to go to Beijing(https://www.travelchinaguide.com/cityguides/beijing.htm) directly from Vancouver, the Home-Visiting Certificate is used to enter Mainland China for Hong Kong residents departured from Hong Kong. But you go to Beijing directly from Vancouver rather than Hong Kong. You need apply for a China visa by using your Canadian passport. However, as I know, many people use the Home-Visiting Certificate to go to Mainland China directly from overseas without problem, only a few people are refused to pass the customs. You can try your luck to enter Beijing by using Homg-Visiting Certificate.

The other option is go to Hong Kong from Vancouver, then use the Home-Visiting Certificate to go to Beijing from Hong Kong.

If you are refused to pass the customs, you have to take the same flight to return to Vancouver, to ensure your trip to Beijing, you'd better apply for a China visa by using your Canadian passport.