Hi, My mom is visiting me in canada and she wants to go visit my brother in China from canada.

If she goes there for a short-term visit, she can apply for a tourist L type. Your bother can issue an invitation letter to her. And then she prepares the required documents including her passport and copy of its data page, the application form, a passport-sized color photo, her valid visa in Canada and the invitation letter. Afterwards, submit the application to the CVASC to apply for it.