1. There is a distinct difference between border crossing with security between North America (USA & Canada) and the rest of the world. Canada has only one border, physically, that with the USA. Easing crossing between the two after 9/11 is not the same thing as integration. Until the USA has Border security on its southern border the subject is nonsense.
2. While some stability in currency would be helpful, integration in currency is not going to happen, the Canadian people would not accept it. The USA is destroying the dollar with debt and QE2, QE3... In the last year the Canadian dollar went from .95 to 1.04 US. Surrendering the Canadian dollar to a common currency is not even on the horizon. If the USA does not stop its debt-based self destruction, it will be even less likely.
3. The economic currency union + currency union without complete political integration(effectively becoming one country) in Europe is destroying Europe. It does not work.
4. Canadians have no more interest in surrendering sovereignty that do Americans. Canadians are if anything paranoid on this subject. Canada has about the population of California, it would be an unequal contest. Beside it would not be in the USA interest to have such integration, to impose, for example the EPA’s idiocy on Canada would cut off 20% of the USA’s natural gas and oil. The same thing would be true for Mexico.
This kind of fear mongering, in the articles mentioned is the pipe dream of radical liberals perhaps but is is also tinfoil.
There's your problem. You're trying to use logic. Logic is a failed western construct of dead white men. The "interest" in question is not pro-USA, and is the same "interest" that has cut off access to domestic oil and natural gas due to EPA idiocy. Therefore, to this "interest," cutting it off in Canada and Mexico as well would be an objective, not an obstacle.