Every year the PM leads a ritualistic blood-letting, and all the anger pours out from each canadian in the form of maple syrup. They bottle it and distribute their soul's malfeasance to other nations. The residual bad-vibes are soaked up by the naturally hate-absorbent Canada Geese, and it is rained down upon the US as they 'migrate' (read: fumigate) over our heads.
(Real answer: I have a theory about harsh climates naturally leading to particularly hospitable cultures. I haven't done enough research to back it up, but it seems like places that are Snowy or Hot or Hard-To-Live-In tend to have really friendly people.)