I haven't talked to anyone at YC about this, have no inside information, and can't read the article, but I imagine this is some technical change about where startups are incorporated. I'm sure applications from Canadian founders are as welcome as ever and there will be no change on the level of which applications get funded.
Seems like a very bizarre move, considering Canadian-domiciled corporations have access to very generous financial incentives (SR&ED) at both federal and provincial levels.
Can't help but think this is a move meant to satisfy the US admin.