Course Access Coordinators can add instructors, e.g., teachers and TAs, to current canvas courses. You can add people by their staff email address or their Login IDs (university UPIs). Please make sure clicking on the Section field and select a section. If a staff needs to be added to the course (all sections), choose the section with the course name. Here is a screenshot of an example:

sections in Canvas courses

Sections

A full guide about how to add users to Canvas courses is available from Canvas Guides.