Originally Posted by
Smiley90
US/Canada are NOT considered sterile.
What some Canadian airports have is what's called a transborder region - you go through US customs at the Canadian airport and enter a "sterile US" area, you then land as a domestic flight in the US. But there's no sterile combined US/Canada area (e.g. if you fly from the US to Canada, you always clear customs before flying onwards)
The post you're replying to is in regard to flights from US/Canada arriving in Europe. They very much can be sterile if the destination country regards them as sterile. (And I'm pretty sure US and Canada are usually regarded as sterile in this case.)
Also for completeness: "sterile" transfers do exist in Canada, but only in limited situations, and only when originating from a sterile country. E.g. flying US->Int'l via Canada doesn't require you to pass security or customs (but you do get immigration), I think they also expanded that for some Int'l->Int'l (possibly if your origin is germany?). If you're destination is US or Canada you do get security as mentioned.