I mean, say, you want a really nice camera, or a drone, or maybe a gaming laptop, and since those things are made in China, they are too expensive to buy right now in the US, since tariffs are over 100%. So you just go to Canada, buy the thing, unpack it from the packaging, and pretend like its just personal items. Just like a smartphone.
AFIAK, border agents usually don’t ask if you bought your phone in the US or from outside, they shouldn’t ask about other personal electronics, right?
Sounds like a trap to me.
By “declaring” I’m not necessarily saying an itemized list of every tiny item you bought, especially if you’re under any limits. But I would be prepared to show all of it if asked. All it takes is one border guard having a bad day to make a difference.
And expressly going to another country to buy a product outside the limits and then sneak it back in to avoid duties is entirely different than some souvenir trinkets and candy.
If you declare the laptop, the border guard might just wave you through without making you pay the duty. If you don’t, and they catch you in a lie, good luck.