I am posting this is the Clean Debate Zone in order to avoid irrelevant emotional and illogical responses. I hope the mods will help out.
1. Economic Union. It seems that Canada's economy is so intertwined with the US economy that maintaining separate rules for each country is an unnecessary and counterproductive distinction.
They Canadians don't think so. They find their laws quite necessary and productive. US financial laws for example are so loose and so poorly crafted that the US financial industry has gone on long cycles of boom and bust with round after round of bank collapses.
Canada's financial industry in comparison is historically far more stable with very few such busts.
No one wants to be the 51st state.
2. Military Union. It seems that maintaining separate military establishments is inefficient and inequitable. By necessity, the US is forced to provide the same level of defense for Canada that it provides for its own States.
That's not true. Canada has its own military. The US military and Canadian military cooperate closely for common defense. The rate of active duty service is about double in the US than it is Canada. Which still put the Canadian active duty percentages at around .16% to the American .38 %
And again, national defense isn't what the US does. The US projects its power around the world far beyond what is necessary to protect its own sovereign borders. Or Canada's, for that matter.
The greatest defense either nation has are the Atlantic and Pacific Oceans.
3. Political Union. It seems that Canada could retain its identity and customs under the US State/Federal system, particularly if Constitutional Amendment addressed this issue.
Or they can retain their own identity and customs without the US. Canada gains nothing they don't already have and lose sovereignty.
Its a poor deal.
4. Other Issues. The idea of Canada becoming the largest state of the USA might create some unintended political consequences. With over 40 million residents, it would have an outsized influence on federal elections. In addition, Quebec would probably be opposed to any union that did not preserve the special privileges it now enjoys from the rest of Canada. (On the other hand, an isolated Quebec would quickly descend into third-world status.)
One possible scenario in which unification might become feasible would be for Canada to be represented by two or more States. The Province of Ontario has about 15 million people, and Quebec has about 9 million, so let's start with them as States. The Maritime Provinces have about 2.5 million, so they could decide to become part of Quebec, Maine and/or Greenland. On the West Coast, British Columbia could join up with Washington, Alaska or Hawaii. That leaves the Prairie Provinces of Alberta, Saskatchewan and Manitoba. They are the heartland of Canada and could join up with their sister States across their southern borders. The Northern Territories could associate with Greenland, creating a solid wall of defense for North America.
I know this sounds outlandish, but maybe we could join in this intellectual exercise and leave our emotional outbursts at the door.
It seems unnecessary and a bad deal for Canada. They already have a great national defense. They have no one who can plausibly attack them due in large part to geographic serendipity. Their greatest threat, logistically, would be the US itself.
They would sacrifice soverienty, culture, a single payer healthcare system, economic stability, bodily autonomy, practical safety, in exchange for what that they don't already have?
Its a terrible deal for Canadians. Which might explain why there is so little support for it. No one wants to be 51st state.