Loblaw Companies Ltd. include Extra Foods, No Frills, Superstore, T&T, Wholesale Club, Loblaws, Zehrs, Independent, Fortinos, Valu-Mart, Provigo, Maxi and Save Easy. As the largest retailer of groceries in Canada, Loblaw Companies Ltd. has a significant amount of power over food suppliers.
Recently, Whole Foods announced that their American and Canadian stores would phase in mandatory GMO labelling by 2018.
If Loblaw Companies Ltd. were to follow Whole Foods' lead, and enforce mandatory labelling of GMO food products through all their food store chains, it would allow the majority of Canadians to actually make a choice as to whether they want to buy GMO foods or not. While this isn't a replacement for mandatory labelling laws, it would be a major step towards giving Canadians choice.
GMO food definition from Wikipedia:
Genetically modified foods (GM foods, or biotech foods) are foods derived from genetically modified organisms (GMOs), specifically, genetically modified crops. GMOs have had specific changes introduced into their DNA by genetic engineering techniques.