Its variety, some nice cheeses mainly.But the other issue is whether there's any point in importing dairy supplies from the other country when both countries are dairy sufficient?
I can see importing rare minerals or other items that are not available in your own country. But Canada and America both have cows. So cross border dairy imports would seem to be a non issue.
I think the tariff and quotas are there to prevent American dairy farms simply trying to bankrupt Canadian dairy manufacturers by flooding the Canadian markets with product and de stabilizing it