The first line of Canadian border guards is trained to ask unexpected and misleading questions. The first few times I went through without a problem, as I naturally engaged in the conversation and, probably, showed expected surprised reactions to the probing. That would be like the grandparent poster explaining how'd he find his friend.
After a couple years I got tired of the game and answered, but shortly. Like: - What are you doing in Canada? - I live here. - Where do you live? - Waterloo. - What do you do in Canada? - See my residence permit, it says I'm a spouse of a student. That's it. - Do you work? - My residence permit does not require me to work, sir. - (starts getting annoyed) Are you working? - Yes. - What do you do? - I'm a university professor. - What do you teach? - My contract does not require me to lecture. I do research. (I later learned to skip this one. Professors teach, everyone knows that.) - What do you research? - Physics. - Where are you coming from? - (name of the country I've been on the flight from). - What did you do there? - It was a business trip, sir. - What business? - University business, sir. - Are you bringing any goods with you? - No sir, just as I have stated in my declaration. - Why? - It was a business trip sir, I did not have time to buy.
After the above, I usually ended up in the immigration office, then a full customs search of my bags. The immigration office would admit me, sometimes with a farewell statement "You are not (sounding) frendly. But that's okay".
Eventually I decided to find out what was triggering the searches, and whether I was at a real risk of not being admitted home after one of my numerous business trips. I requested at the first check to be routed to the immigration, and had a long conversation with the immigration officer. I asked to clarify things. The Canadian officer asked me lots of questions, explained the law permitted them to deny me entry (because I didn't have permanent residency) but they saw no reason to do that, and stamped my passport. Then the female officer switched language and told me in clear Russian, which I translate here: "When a weird-looking bloke in a t-shirt with long hair and discheveled beard says he's a professor, we have to investigate". Well, these reasons are not something I can fix :).
This is the only country where I'm regularly interrogated at the border. In Europe and the rest of the world, the guards either silently look at my visas and ask nothing, or ask 1-2 quick questions about the duration and purpose of the trip. Customs have never been interested in searching my usual luggage. To me, Canada is a stark contrast to the rest of the world.