Just to point out in respective of at least "Loblaw" they own a lot more than just grocery stores and just using the profit margin is not a absolute indicator of how profitable they truly are.

Loblaw Companies>George Weston Limited>Wittington Investments, Limited

Report regarding grocery inflation.

We know very little of what is going on in food processing, transportation, and at other companies who participate in the food industry. A proper investigation led by the Competition Bureau of Canada would shed some light on practices in the industry.