Isn't that already the practical reality when the USA has unfettered access to sell the food the animals eat in Canada? Having control over the milk supply doesn't offer much when you don't have any live cows in which to produce it with. I remember what Canadian dairy farms did during the US corn subsidy heyday (hint: they happily bought the corn that sold for less than it cost to produce). Canada is only fortunate that the US backed off on those subsidies a decade or so ago, but that could very easily reverse again, especially if there ever became motive to sink another country.

> We now know that if we allow other countries to have undue leverage over us, they will eventually use it against us.

Doesn't that make dairy an especially poor food to weather conflict as it is quite hard to keep from spoiling? Your case might be stronger if we were talking about wheat or something like that which can sit idly in bins for long periods of time, but there is no such protections on it or anything else other than poultry and eggs which are also hard to maintain.