Users in canvas can have multiple roles, that are different based on the context the user is in. For example a user could be a teacher in one course and a student in another. Or a user could be an admin in one account, and not another.
There are two different endpoints you will need to look at to check what roles a user has.
Enrollments:
https://canvas.instructure.com/doc/api/enrollments.html
An enrollment object in canvas will tell you what courses a user is in, and their role in the course.
Admins:
https://canvas.instructure.com/doc/api/admins.html#method.admins.index
The admin endpoint can give you a list of the admins in an account. But you will need an access token that has admin permissions to access this API.