There are theoretically ways to import butter to Canada, but you need a special license, and there are very strict quotas. Generally, only large dairy corporations can get them, and only to handle major shortage.
In my entire life spent mostly in Canada, I have never seen butter being advertised as being from another country. Cheese, definitely, but never butter.
Even trying to bring some home with you from a vacation isn't allowed. It would be taken if declared at the border, and destroyed. Failure to declare it is a crime.
Why? The Canadian dairy industry is an incredibly powerful lobby group. All they have to do is point to the very low standards in the USA and say "if we let foreign dairy in, we'll be exposing Canadians to that". Liberal governments and Conservative governments alike pander to them endlessly.