Customs officials in all countries have broad latitude to inspect incoming passengers and baggage. Fucking around with them and refusing to answer or evading questions is franking a stupid strategy.
What has changed is that there is more inspections and more theatre. They are more consistent(-ly awful) everywhere, including sleepy Canadian broader crossings.
So one year, after having moved to Seattle, I thought I could drive the gift across the border, make my declarations there and then mail it from Surry, BC. So I took my gift -- unwrapped -- in it's shipping box -- untaped -- and drove to the border. When I got to the window they asked why I was visiting Canada. I honestly told them that I was coming to ship a package and explained why.
I spent the next three hours sitting in a waiting room while they went through my cell phone, they went through the open box I was going to mail, charged me import duties, went through my car from top to bottom. Eventually they sent me on my way. I drove ten minutes to a UPS store and mailed the package.
Returned to the US, when I arrived at the booth, I handed them the paperwork the Canadian side had given me, they noted the time and asked why I had visited Canada and why it was only forty-five minutes, I explained that I was mailing a package, handed them the receipt from the UPS store and explained why. They laughed and waved me through.
Border crossing can be hit or miss depending on the mood of the agent.
Of course, this might just be luck of the draw.
They would ask me questions like "how long are you going to be in Canada?" when I'd answer that I didn't know, they would press me about why I didn't know. One guy who had held me up for far too long, I basically told him "I'm Canadian, you don't have an option to let me in or not" at that point, he let me through...
Be careful with that - while they have to let you in, your stuff is another matter.
I'm kind of surprised that this was even a question for a Canadian citizen.
American guard is like "do you have more than 5 bottles of wine you need to declare? No, cool"
Contrast with Russian customs who looked at my passport and said "Canada? Okay go"
Flying into Toronto City airport I frequently just get a nod and hand wave.
When I get to the Canadian border, once they realize I'm Canadian, everything changes. It's a very friendly, warm greeting like a couple of old buddies that are heading out for a beer. My American wife, who's watched this a ridiculous number of times is just blown away by how I'm treated.
However, at the US border, while not always bad, I have run into several border agents that have been pure assholes. I've been detained and searched a number of times and have always been polite to a fault - I'm as white as the driven snow and have never broken a law, or been arrested. But you would think I'm flagged as a suspected drug runner or potential terrorist sympathizer. Sadly, it's simply not a stereotype.
I had no passport, and the Canadian customs didn't ask for one.
The Canadian customs officials were all women, looked friendly, and were smiling. It looked like Canada was a really nice place!
So, I joked, self deprecating, that here I was, a US citizen from the crass, crude, violent, insensitive, vulgar US! :-) Right away with some seriousness of agreement the Canadian woman concurred! Still, it was a nice trip to Canada! I like Canada and hope to go back!
Of course, next time, in trying to return, maybe the US customs won't let be back in!
I think it depends heavily on the crossing and the specific staffing there. You have two jurisdictions sort of working side by side, so there's lots of fodder for tit-for-tat bullshit.
Now, this only applies to US citizens returning to the US. A US citizen arriving, for example, at Amsterdam, can certainly be turned away for any reason whatsoever.
Here is the lengthy document I remember: https://www.eff.org/document/defending-privacy-us-border-gui...
They can demand a password from you, you can refuse to give it, and they can then decide not to let you in the country. Being polite and respectful in your refusal to share an encryption key can mean less trouble.
A point that might have caused confusion: they can seize your device. The document does not specify what happens if you decline to give the device (as in whether you are arrested or simply declined entry to the country). As far as I understand the references, courts have not had to decide on this question yet.