The idea to have the US pick on Canada, internationally one of the world's least offensive and bellicose countries is itself brilliant. It wonderfully picks on the US, and more generally, on any rather belligerent nation that likes to throw its weight around and create excuses for doing so.
It also picks on the use of propaganda and even on mass media and mass mob hysteria. This is especially true in the way the film portrays how the American media discusses Canada and how some members of the public react, so that the whole idea spins out of control of those who began it for their own personal reasons. I was barely able to breath with laughter throughout the whole period when the US was flashing its propaganda about Canada and showing how threatening they are, especially how they claimed the Canadians were "infiltrating" American society and were "massing" on the border. This is wonderful satire on sensationalist news stations and their willingness to use information in a wildly inaccurate and misleading manner in order to rile people up.
The film picks on everyone involved, Canadian and American alike. It attacks the stereotypes of both, highlighting their differences yet also attacking the misconceptions about both peoples. To have a number of Canadians in the film is another flash of inspiration, too, since there are Canadians playing comically stereotypical (i.e., polite, white bread, well-spoken) Canadians and Canadians playing comically stereotypical (i.e., redneck, belligerent, crude) Americans. It adds to the irony since one of the American's propaganda tools is that there are Canadian actors everywhere in the US as such integral parts of the American entertainment industry that they are taken for Americans, and lo and behold, here some are playing various people in this film.
Some parts of the film were simply silly, with jokes that were more gags rather than actually furthering the satire and points of the movie, and this is a weak spot. While some were funny and worked, others were a bit inane and the film would have been more successful had they stuck to developing the real themes and satire of the film, which are what make it great.
Anyway, despite some weak points, this film is a brilliant satire that contains a number of parts that are utterly hilarious. It did not fulfill its full potential, but it is not too far below perfect and the good parts are really, really good.