For a recording to appear in Canvas, two things must occur.
1. The conference must have been started with Enable recording for this conference enabled.
A key point is this option must be enabled before starting the conference. (If the instructor starts the conference, and then while the conference is running goes back and enables this checkbox, it won't have any effect).
If you want this box checked by default, see Enable all conferences to be recorded by default.
2. During the conference, a moderator must have clicked the Start/Resume Recording button to mark the start of recording at least once.
If the instructor does both (1) and (2), then shortly (within 24 hours) after the conference concludes, the recording should appear.