As a Canadian who has lived in the US for the past 10 years, and crossed the border "home" at least 5-6x per year, let me tell you that you don't know nasty until you've upset Canada Customs and Revenue.
Truthfully, they have extraordinary powers (makes the BCIS look child-like), and they're not afraid to use them. Of course, you do have to know what you can and cannot say.
A great example of their attitude problem can be summarized with this little question(happens on 30% of my entries into Canada):
Hello Mr. Gabrielz. What's the purpose of your visit?
My visit?!?!?!

I'm Canadian for crissakes.
So, the last time I got asked this question, I pointed that fact out and told the inspector I thought the question was absurd. He agreed.
Then he threatened to send me to secondary.
Nice, eh?
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