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.