The WSJ had an article on agriculture in Greenland a couple of weeks ago. Strawberries, certain trees, etc. Not much, but a start. There was an earlier article on the growing wine-grape region in BC, Canada. Parts of France are now too warm for the vines.

Guess it depends on what is being grown/raised, but my vote goes for the above-mentioned Sami reindeer herders if this is the "any" category of agriculture. There isn't much north of that unless it comes from the sea. In the "crops" category, do any cereals grow further north than Sweden or Finland?