It's partly an affected practice, yes, especially among people my age and younger. But it does come from somewhere - parents or grandparents who still speak this way, for whom it's more of a geographic/identity reference than anything else.
In the identity sense...
If a middle-aged woman here is telling friends about her new son-in-law, saying he's Canadian instantly tells them a paragraph worth of information - most importantly that he's not from here. They'll fill in the blanks with the stereotypes everyone recognizes (positive ones too), share knowing smiles, and all that's left for the middle-aged woman to articulate is how that instant impression is incorrect. "But he's got a wicked sense of humour and he's witty enough to put anyone to shame.", etc.
That's the way it still survives, for the most part. And it proves useful.
In terms of geography, it exists as short-hand for "the rest of Canada". When someone in their 20s here says they're going to work up in Canada, they don't really mean we're not - they just mean the mainland. They could just as easily say "upalong". They can even say "mainland" or "away", but those doesn't specifically reference Canada. Mainland could be the U.S. as well, and "away" could be literally anywhere else on earth.
So you'll see this type of reference quite often as well - but, again, it's not political.
But, yeah, of course there are people who do it like this:
http://failblog.cheezburger.com/failbook/tag/swastika
I met a woman who claimed she wasn't Canadian because she voted against it and never signed anything. And it didn't seem to be just a case of mental illness.