On Monday more than 30 flights, including ones to New York, Newark, N.J., and Philadelphia were showing as cancelled on the departure board at Pearson airport.
About two dozen flights Porter Airlines flights have been cancelled between Toronto and Newark, and Toronto and Boston for Monday and Tuesday.
Forecasters say the storm has the potential to break records and dump more than 90 centimetres on some parts of the U.S. northeast.
As of noon Monday, more than 2,500 flights originating in the U.S. been cancelled, according to the flight tracking site FlightAware. Another 3,300 flights have been scrapped for Tuesday.
New York City Mayor Bill de Blasio warned residents not to underestimate the storm and asked people to not come to work Monday if they could avoid it.
The heavy snow is expected to begin this afternoon and continue through the night with blizzard-like conditions in the forecast.