Students are added to their classes eight days prior to the start of the quarter. Students then have access to published classes seven days prior to the first day of the quarter. If faculty have not published the course, students will not have access. Not all face-to-face classes use Canvas. If you think you should have access and it is after the first day of the quarter, check with your instructor to make sure they have published their course.
The ability to authenticate in Canvas is an overnight process. If you register today, you will not have access until tomorrow.