Maybe follow the Australia example and only allow 4000 international arrivals a week. Add to that Australia bans all international travel out of the country unless maybe compassionate. In effect the country is currently closed to the outside world as far as travel is concerned and with the arrival number restrictions even citizens and PRs have issues returning.
Cannot see either working for Canada so the alternative is maybe stricter health assessments of transit passengers as opposed to transits quarantine at POE given if nothing else the numbers quoted. Anyway who is to say a domestic passenger is not flying whilst infected.