Well, I have never gone through the US or EU citizen questions, being Canadian, but I have entered Canada countless times (almost all my flying is international), mostly through YYZ T1 or T3, and occasionally through YUL, YKF or YVR. I have to say that I cannot recall a rude CBSA agent, and there have definitely been many that have been friendly. Often all it takes is one friendly comment when you hand over your passport and form, and the interaction becomes more pleasant. Questions not relating to the form are typically limited to asking where I'm arriving from, and sometimes what business I'm in. And the similar experience applies to land crossings (I fly from BUF from time to time as well).

US immigration, though, at least as a Canadian citizen, has been far less pleasant in my experience. I usually have the feeling that I am being treated guilty until proven innocent, and I generally do not dare make any comments other than 100% factual answers to the questions. The displeasure of answering US immigration questions was, in fact, the prime motivator for me to finally apply for the Nexus card (still in progress).

Overall, my CBSA experience is definitely on par with countries like UK, Australia, New Zealand and Japan, and far better than the US. However, there are definitely fewer questions being asked at EU Schengen countries -- at least of those of us with Canadian passports. And no customs forms needed for EU!