Guys, thanks a lot for your replies. It's certainly very reassuring. I'm a citizen of one of those "certain" countries.
However, there is something that really concerns me. Here, someone says they handwrite "flag-pole" as the third option in the "refusal" form: http://www.canadavisa.com/canada-immigration-discussion-board/landing-procedure-t34798.0.html;msg222174#msg222174
But in my case they explicitly marked the first option: "Refused admission into the United States".
That thread is from 2010. Is it common to mark the first option nowadays? or do they still have the practice of the hand-written "flag-pole"?
Thanks!