This page reviews how to allow specific students to access a course after the term ends in order to finish an incomplete. It also explains how to properly "close" a Canvas course and what restrictions that introduces.
It is not recommended that instructors keep courses "open" merely to have access to the materials to use in future courses. Doing so keeps the course open for all the students, which they may not want to see. Instead, instructors should create a 'sandbox' shell in their account with no enrollments and store the course materials there.