The US is actually buying many of its armored vehicles from Canada. Most of the world is standardizing the technology in armored personel carriers and fast attack vehicles. and Canada has been pretty succesful building them.
Regardless, missile defence is so bullshit. The first few rounds fired in a nuclear war will likely not be as clean as people think. Any commercial airliner that clears customs in it's native country could theoretically just be a shell for a nuclear weapon. With that sort of device, you don't even have to land the plane, just fly it over a city at a certain height and press play.
Other than that, how many thousands of miles of unguarded coast is there in north america? Hell, load a weapon on the back of a 1/2 ton in Canada, drive it across a farmer's field at the border in Manitoba / North Dakota and then it is pretty much clear sailing all the way to a metropolitan area.
How many containers on a container ship do you think customs actually checks? Hell, if found out, detonating a weapon on a container ship in port would do significant damage to the surrounding area.
Its sad how undefended the world really is and a space based piece of shit isn't going to do dick to someone with the means and the motivation. Lets hope to hell it never happens.