The Retail Council of Canada says the weekend storm arrived at a make-or-break time for many stores' profits, with $30 to $40 billion in sales rung up during December.
It says the final tally of business lost to the weather system that toppled trees, interrupted transit and left hundreds of thousands without power could be high and have a huge impact on small- and medium-sized retailers.
The group says stores are trying to be flexible by extending hours and is asking shoppers to check if their local merchants are staying open later.
One recent arrival on the Canadian retail scene has stretched its operating hours to accommodate shoppers looking for last-minute Christmas gifts or storm-surviving staples such as batteries and candles.
Target said some of its stores in Ontario and Atlantic Canada would remain open until midnight Monday.