Canada

And when they don't come to Canada's assistance? When they decide that necessary assistance is to condemn US aggression and send Canada a "get well" card?

Article 5 was written with Russia in mind. The penalty for noncompliance would be a natural consequence that Russia would feel free to pick NATO countries off one at a time. It's entirely ineffective against a US that literally could fight off the rest of NATO if it had to.

Maybe you'll believe the Center for European Policy Analysis

The Article 5 wording is vague. It states that an attack against one member “shall be considered an attack against them all.” What is quoted less often is that each member state only has an obligation to take “such action as it deems necessary, including the use of armed force.”

In other words, Article 5 does not commit member states to deploy military assets if an ally is attacked. It only commits them to some form of response.

But, what do they know anyways?

Did you miss where "mutual assistance" is completely undefined. I'll stick with my original answer. I'm sure NATO will come right to Canada's assistance with an angry condemnation of US aggression at the UN.

Laws with no penalty clauses aren't really laws, they are suggestions. Penalty clauses that can't be enforced would be worthless anyways. Article 5 is an aspersion, nothing more.