Yes, you are absolutely right that the food supply is critical infrastructure. Under Public Safety, there are a number of plans for the various sectors. There's an emergency function that exists for food and water. Of course, it is thinking more in terms of localized, regional crises that require a punctual intervention to procure food and water for a specific situation, whether it's an area affected by flooding, etc. Having a comprehensive plan to deal with the magnitude of the COVID-19 situation, I don't think any plans could have anticipated that. However, as you pointed out, it was key to designate workers in the food area as essential from the get-go.
On November 19th, 2020. See this statement in context.