From what I've heard, Canada is actually a lot worse than the US.
I was traveling as part of a party of five (different travel dates, separate ETA filings, no apparent connection). One of us didn't get an ETA. Another got one just before the trip (and it was a 13-year-old child). The rest of us got ours immediately, but I was questioned at the border for 10+ minutes with no apparent reason, and then allowed in without a comment.
From what I heard anecdotally, Canadian officers are trained to “interrogate” everyone believing the added duress will cause people to slip up and reveal they are really a terrorist or some such.
I'm a US citizen, living in the EU and have global entry, etc... I've been to Canada once on business and they asked more questions than I've ever had asked on all my frequent travels back and forth EU-US.