Environment Canada issued snow warnings for southern Ontario and southern Quebec, while a freezing rain warning was issued for central and western New Brunswick.
High wind warnings were issued for Wreckhouse, N.L., and Inverness County, N.S.
The main storm affecting the regions began in Ohio and was expected to march east along the Great Lakes and St. Lawrence River.
Ontarians felt their first taste of the storm as freezing rain struck areas from London to Toronto and Kingston overnight Wednesday. The rain was expected to turn into snow later Thursday morning.
"Travellers should be prepared for significant deterioration in driving conditions with hazardous winter driving conditions likely today," Environment Canada said in the weather warning it issued for Ontario. "Very low visibility at times and heavy snow is possible."
Toronto is expected to get between five and 10 centimetres of snow by the end of the day, while areas like Barrie, Kitchener and Peterborough could see 10 to 15. Ottawa is expected to get 15 centimetres.
The snow started falling in some parts of southern Quebec Wednesday night, with between 15 and 30 centimetres expected in Montreal, the Laurentians, Quebec City, the Saguenay and the Gaspé.
In some areas, the rain will turn to snow, with between 20 and 30 millimetres expected to fall in the Eastern Townships and eastern Gaspé.
Airports in Montreal and Toronto began to delay and cancel flights on Thursday morning, while school boards in Ottawa, York, Halton and other areas cancelled bus service, though the schools remained open.
The storm was expected to spare most of Atlantic Canada, except for New Brunswick, which will likely be plagued by freezing rain Thursday night. The eastern side of the province, including Saint John and Moncton, should be spared.
The rain will likely turn into snow on Friday.
"Icing problems will develop as freezing precipitation persists for many hours over central portions of the province," Environment Canada said of New Brunswick