How can I get a Canadian marriage certificate notarized by Chinese Consulate? Could I mail it?

You can either walk in to submit the application for notarization and get it back or entrust someone else or travel agents to do it for you. If you entrust others to do this, the original and a copy of both the entrusted person's and your passport are required. Mail application is not acceptable. Make sure that the document should be first authenticated by the authentication office of the relevant province (territory).