Start by explaining your situation.
Police background check
Diploma certification
Going to the Mainland to teach English. How do get the things that can be done in Taiwan, done in Taiwan?
Mention that you also have a Taiwanese passport, along with your Canadian.
Will I get my visa through here, or in China?
Ask about the steps of the visa application process. What things to watch out for, about how long it will take, what things I will need to do after obtaining the police background check and diploma certification.