Spoilers: It was because of anti-communist sentiments and policies.

Canada’s Immigration Department after the war determinedly and successfully prevented communists and other leftists from immigrating to Canada or even visiting the country.

...

My interpretation of the immigration files, along with cabinet discussions, is that the same anti-communist obsession that dominated immigration policies before the war and resulted in indifference, if not actual support, regarding fascists and Nazis who might be entering Canada, quickly re-established itself after the war.

Right-wing extremists, rather than being viewed as a security threat, were viewed as potential docile workers who would be on the “right side” as Canada made the fight against communism internally and worldwide the centre of its foreign policy. They would be bulwarks against Marxism and Marxists in Canada.

The government actively chose Nazis over communists, Jews, and people of colour, because Nazis would oppose communists, Jews, and people of colour.

I'm shocked. Shocked, I say.

Goddamn it Canada, you weren’t supposed to do your own somehow dumber Project Paperclip.

Might explain in part why this sleepy ideology has been popping up and taking hold so strongly lately. Hopefully they all meet the same end as their ancestors and our society can rid itself of the hateful thought. Looks like we're in for a hell of a fight, though it seems only 10-20% are so hard lined they'll die on that hill.

They also let in the remnants of the Confederacy, including Jefferson Davis into Canada after the civil war. That's why we have Confederate flag waving hicks in Ontario.

Canada has a problem with trying to play neutral by aiding the bad people in a conflict.

What immigration files is the author referencing?

Ah, no wonder they're exporting their fascist trash to the states these days. Had to cultivate it somehow.