Pet waste can still be collected in plastic bags - bread bags, produce bags etc are a good size. Residents can buy bags especially for pet waste. Pet waste (in any type of plastic bag) is accepted in Toronto’s green bin.
*Note, you can buy compostable bio-plastic bags designed for pet waste, but they will be removed along with all other plastic bags during the processing of organics, and sent to landfill as residual waste. In the landfill they’re not likely to ‘compost’ due to the absence of light and air, so there’s no major environmental benefit for using compostable bags.