More than 370,000 US homes and businesses and some 115,000 Canadian homes were still without power Tuesday morning after a weekend ice and snow storm rolled across the northeast.
More than 7,000 flights were behind schedule by Monday night, many of those in New York, Washington, and Chicago as people struggled to travel before Christmas.
At least 11 people in the US have been killed in the storm.
In Canada, police said two people in Ontario are dead from carbon monoxide poisoning after using a gas generator to heat their blacked-out home northeast of Toronto. In Toronto alone Monday night, 11 people were taken to hospitals with signs of carbon monoxide poisoning.
The region was under a cold alert, with temperatures expected to be well below freezing Tuesday.
Toronto Mayor Rob Ford said 115,000 customers were still awaiting power, and officials said some may not have it restored until after Christmas.
Some US states kept emergency shelters open for people who would be without power.
About 250,000 of the people without power were in Michigan, whose largest utilities said power won't be restored for days because of the difficulty of working around broken lines.
In Maine, the number of customers without power spiked to more than 100,000.
Untreated roads and sidewalks will remain a slippery, dangerous mess.
Associated Press writer Charmaine Noronha contributed to this report.