On Friday, the hurricane status of Fiona was lowered to a tropical storm.
However, severe rain and winds of up to 160 km/h (99 mph) continued to batter portions of Nova Scotia, Prince Edward Island, and New Brunswick, bringing down trees and powerlines.
The serious nature of the situation was noted by Prime Minister Justin Trudeau, who also pledged to use the army to support civilians.
Authorities are coping with heavy flooding, although they have not yet disclosed any reports of fatalities or major injuries.
There were tropical storm advisories for areas of Quebec as well as the Atlantic provinces of Nova Scotia, Prince Edward Island, Newfoundland, and New Brunswick.
Up to 10 inches (25 cm) of rain might fall in the country's east, raising the danger of flash flooding.
In Halifax and Cape Breton, Nova Scotia, shelters were set up so that people might seek safety before the storm.
Canada rarely experiences strong hurricanes because, as they reach the cooler waters of the north, storms lose their strength and transform into post-tropical systems.
Fiona will be more powerful than Hurricane Dorian in 2019 and larger than Hurricane Juan, which also made landfall in Nova Scotia.