Canadians Are Racist. They don't like Black people.
Current Canadian immigration law favours non-Blacks. The point system, allocated for university education and related work experience, clearly puts African Americans, and other Blacks, at a major disadvantage. Family reunification favours non-Blacks, because there are few Black families in Canada to be reunited to. And I don't even need to bother mentioning the entrepreneur and "investor" classes.
Europeans can work in each others countries. NewZealanders and Australians can work in each others countries. But American (10% of whom are Black)? No way, they must stay out. The border guards now even have guns to protect us from them.
If Canadians weren't so racist and so afraid of the 33 million Black Americans, Americans would be allowed to live and work in Canada.