Including their brandname chains:

• Atlantic Cash & Carry
• Atlantic Superstore
• Axep
• Bloor Street Market
• Dominion
• Les Entrepôts Presto
• Extra Foods
• Fortinos
• Freshmart
• L'Intermarché
• Loblaws / Loblaw GreatFood / Loblaws CityMarket
• Lucky Dollar Foods
• Maxi / Maxi & Cie
• NG Cash & Carry
• No Frills
• Provigo
• Real Canadian Superstore
• Shop Easy Foods
• Shoppers Drug Mart / Pharmaprix
• SuperValu
• T & T Supermarket
• Valu-mart
• Wholesale Club / Club Entrepôt
• Your Independent Grocer / Independent CityMarket
• Zehrs Markets

Yes there are other big oligopoly chains like metro, Sobeys/Safeway, Pattison, but I think it's best to start with one major chain to see how much coordinated action can affect them.