Are you familiar with parallel construction? That's what this is for. If they have a warrant and show it to you, it says what they can search and why. If they don't tell you what they're searching for and why, they can look for anything, and then construct a separate scenario which just happens to expose the thing they knew would be there from the first fishing expedition. They then use this (usually circumstantial) evidence to accuse you of a crime, and they can win, even if you didn't commit a crime, but it looks like you did. And now they can do it with digital information, automatically, behind the scenes, without your knowledge. (or they can take your laptop and phone and do it then)

i know this is an american thing, but does it actually happen in Caanda?

But the warrant still has to originally exist with, presumably, a timestamp that shows it existed prior to the search. And modification of the timestamp or lack of such a feature would be a good way to get the evidence thrown out?