It won't happen.
Americans are too ingrained to their Constitution and Canadians are too ingrained to their Charter.
Americans are ingrained with their right to bear arms while Canadians are more relaxed on recreational drug use.
Americans fear anything towards going back to any sort of Monarchy / British reference towards Government and would more rather join France.
The person who wrote this "Canada to the Rescue" the OP linked is obviously American and has an American Attitude towards the merger concept.
"This used to be a very tough argument to make, because most Americans were unwontedly proud of their political system."
^ And Canadians aren't?
"We should not, of course, underestimate the difficulties and complications. Would Canada’s provinces become states, with two Senators each and proportional inclusion in the House? How would the different health care systems be managed in a union? What about significant alternative legal approaches to various functional issues, not to speak of the U.S. Constitution itself? Obviously, a union would need to be sequenced into being over time, and a group of Wise Men (and Women) would need to be in operation for several years."
^ Why would Canadian Provinces become States? Why don't American States become Provinces? If the US system is so screwed up as this writer states, then why does the writer automatically assume Canada and its provinces would assimilate into the screwed up US system??
^ Why would Canadians adopt the US Constitution and not the other way around?
^ Why should Canadians break away from the Monarchy and the Commonwealth just to please Americans?
^ Or how do you properly manage a completely new system that is some Frankenstein combination of both types of government to make both sides happy?? (Is that even possible?)
Indeed, what about the laws and punishments in each legal system?
Canadians use the same English and Spelling as the UK, Australia and other nations while the US uses their own spelling/English.... who adopts what?
What about the distribution of each country's natural resources, lands and even jobs and careers?
How are Canadians to believe that they won't become second class citizens in what once was their own country and land?
What are the actual benefits for Canada in a merger?
Cheaper Books at the Bookstore??
Besides somewhat similar accents, driving on the same side of the road and WalMart, Canadians have more in common with Australians than they do with Americans, which I know first hand after spending a few years living here in Australia.
How about the US first merges with Mexico and see how that works out before talk of merging with Canada?
The reality is that it's never going to happen.... at least not for another few hundred years.
Americans will in no way give up their way of life, their Constitution and their "Freedom" and Canadians are more proud of their way of life than most Americans seem to realize.
There are simply more benefits and less headaches in keeping both countries separate while helping each other out from time to time, than trying to sort out a nightmare of trying to merge both countries together and avoiding both societies going after each other's throats for having their way of life taken away from them.
To think merging both nations together is a good idea is beyond short sighted.