The university's international office is usually the quickest route for this. Health cover for international students often differs from what residents get, and it varies by province or region, so it's worth confirming what the university plan covers and when public cover starts. The Healthcare section for Canada covers the general rules.
My daughter started university in Canada this month, and the student health cover was more confusing than I'd imagined. The university had its own plan, which was automatic, and then we discovered that the provincial public cover worked differently for international students, and there was a waiting question we hadn't understood.
For parents or students who've done this: what did your university actually require, and did you need anything on top?