Admiral Beez
Superstar
We already do this. Airlines across the globe cannot fly anyone to Canada without proper permission to enter - and they are charged fines by Ottawa for boarding anyone without correct documents. In the 1990s I was an customs agent at Pearson and often experienced refugee claimants who seemingly boarded with proper papers but destroyed them before they got to me. As you suggest, the Visa-exempt list, as shown here can and is adjusted from time to time. We do this now.There can be a throttle. When refugee claimants from Mexico got extremely high, they introduced a visa requirement for some so that people getting on a plane from Mexico to Canada are checked out by the Canadian embassy before they're allowed to do that.
As there is no other throttle to reduce migration, we are lucky to have oceans on three sides and a belligerent, anti-migrant America to our south. Otherwise we'd be overrun like when the wight army marched into Westeros. Though we'd best be prepared for a northbound horde of illegals residing in the USA fleeing ICE.
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