Instructors of courses on Canvas's Instructional instance generally have to use one of the following workarounds:
1) Work with the Registrar to change section enrollment in the Student Information System.
At each institution, the Registrar's Office creates and modifies sections in the SIS. If course sections aren't arranged in a way that allows the instructor to effectively teach the course, then modifying those sections and enrollments in the SIS is the most direct solution. Section enrollment changes in PeopleSoft will appear in Canvas immediately for some institutions and after an overnight migration process for other institutions. Contact your Registrar's Office for more information.
2) Use supplemental course sections cross listed into the course
Each institution has access to a "Supplemental Courses" subaccount on the Instructional instance. This is a subaccount for courses and sections which are not managed by the Student Information System. This allows for manual enrollment of students in supplemental courses, and the sections from those supplemental courses can then be crosslisted back into the main course.
Here are the steps:
Note: not every UW institution allows instructors to cross-list sections in Canvas. If you don't have this ability, please ask your campus Canvas administrator to cross-list the sections.
3) Use Canvas's Groups feature.