Why did I get searched at the Canadian border?
Why did I get searched at the Canadian border? Why Would You Be Searched at the Border? Border officials have complete discretion as to whether to allow you to cross the border. Similarly, they can decide to undertake a search based on their own instincts. A search can also be triggered by something in your personal record.
How do customs decide who to search?
They don't put their entire trust in people's good character, of course; customs performs a thorough search of some percentage of all travelers. Some customs agencies decide which travellers to search based on random chance. You are asked to press a button on a machine that activates a random number generator.