>we’d supply manage primary food energy like beans and oats
We have enormous amounts of these crops, are hyper-competitive in them and fully self-supplying, and moreso they're very quick to turn around: A single season can yield enormous stockpiles of beans and oats.
That isn't true for dairy farms, egg operations, and so on. These don't scale up nearly as quickly. If Canada allowed the unrestricted flow of US options in these industries, US booms and mass industrial operations would wipe out Canadian suppliers, leaving us hugely vulnerable.
Like in the near future we might have an entire collapse of trade between the countries (as some new nonsensical exercise of brinksmanship is pursued, with new and ridiculous demands). We could wipe out 100% of foods that the US sends to Canada and be...perfectly fine, including, thankfully, poultry, milk and eggs. There are a lot of countries where this sort of food security independence isn't true.
Recent events have amply proven how critical Canada's protection of these industries are, making it all the more ironic that they're such a target. For obvious reasons.