I'm well aware why this is a political decision yet the Canadian PM and his immigration minister stand in front of TV cameras claiming policies are based on safety which in fact they are not, they are political decisions.Once again, US citizens get some preferential treatment because of the unique relationship between the two countries, and the similar benefits Canadian citizens enjoy. Canadian students don't even need F-1 visas to attend American schools.
Apart from the USA advantage, you have the scenario that those with study permits approved before 18th March apparently have some immunity compared to students whose study permits were approved after 18th March (the only ones I've found on this forum in that position came through IRCC NYC and HKG) or still waiting to be approved. Again a decision based on politics not any science.