Water levels continued to rise on Saturday from Toronto and Lake Ontario up to 500 kilometers (300 miles) downstream of the St. Lawrence River, especially in Quebec province, where some 400 troops have been dispatched.
The worst is yet to come, Quebec Premier Philippe Couillard warned on Saturday.
"The water will continue rising over the next two or three days," he said after visiting the town of Rigaud, east of Montreal, which has been flooded for more than a week.
The government ordered the troop deployment on Friday.
"Our troops are responding quickly and professionally, and are already beginning to deliver critical support to Canadians affected by the flooding," Defense Minister Harjit Sajjan said on Saturday.
Torrential rains have added to runoff from melting snow that has caused rivers to overflow their banks, posing a critical situation from Ottawa to Montreal.
The emergency services warned that rising waters would reach regions east of Montreal, where precipitation by Sunday night could reach between 90 and 125 millimeters (3.5 to 5 inches).
Near the Atlantic, the New Brunswick Emergency Measures Organization warned residents to remain on alert until Monday, saying water levels are near or above flood stage in many regions and expected to rise.
In Quebec, the province hardest hit by the flooding, more than 1,500 homes have been flooded in 121 towns and cities and nearly 1,000 people evacuated, the emergency services said.
"I understand people are reluctant to leave their homes," Couillard said, "but if you're asked, do it for your own safety."
