Calgary and Edmonton grew up without local food systems for the most part - we've had the railway forever. I read at the Revelstoke museum that until the dams flooded the land, much of Calgary's 'local' vegetables were from the valley south of Revelstoke. I don't see any need to protect agricultural land beyond what can be accomplished through the regional bodies, control of water, and the South Saskatchewan regional plan.
Now, the Wildrose played significant footsie with the development industry and land owners about eliminating those constraints back in their day, so we shall see where a possible future government would go. Usually since it would incentivize jurisdiction shopping to the Nth degree all the small urban municipalities would fight it as well. Calgary would do well to not push further than those communities can support (the 8 unit per acre standard for connecting incremental development to the water system, while low for urban purposes does force development to not sprawl endlessly).