Hey Craig,
I’m not sure who you’d have to meet to get a job teaching math in Chengdu, but I’m guessing it would be easier to make that connection if you’re in Chengdu. Teaching English is very easy to set up as you probably know. Tutoring math on the side is definitely possible, a lucrative demographic for you might be Chinese students who are preparing for overseas study.
If you’re coming from Canada you can get a tourist visa processed there and switch to a work visa when you’re in China, or you can purchase an F-visa (business) if you will come to Hong Kong before entering China.
Another option