In Quebec, violent winds as strong as 90 km/h in some areas, accompanied by heavy rain, left more than 300,000 lacking electricity.
Those same winds struck Ontario earlier in the day.
In the Montreal area, the winds toppled multiple trees, knocked down power lines and street lights, and sent chunks of debris swirling into the streets.
The main areas hit were the Laurentian Mountains and the Montreal area. But Hydro-Quebec said there were also a smattering of outages in other parts of the province.
The power utility said it was evaluating the damage to the network and wasn't immediately sure how long repairs will take.
The winds were expected to die down later Friday night.
Hydro One crews were also working to restore power to roughly 126,000 customers in central and eastern Ontario late Friday, but warned it would only be able to complete the work as late as Sunday.
The worst hit areas are Bracebridge, with 17,000 customers affected, followed by Huntsville, Kingston and Parry Sound, each with 13,000 customers without power.