Others can comment if they have a different view but The catch is that CBSAs primary role is to protect Canada’s borders and not to issue permits that have not been preapproved by IRCC which they often do reluctantly. Hence for example the restrictions across the Ontario border with the US where they will only accept flagpolers on Tues/Weds/Thursday through specific hours Given traffic volumes outside these days.
If everyone turned up to flagpole then at some point both USCBP and CBSA would likely close down the option for anyone not preapproved completely as a distraction from their primary mission.