The storms uprooted trees in various areas, crushing a man and an older woman.
Another woman in her fifties drowned in the Ottawa River when she was in her boat, CBC reported.
The fourth individual died in Ottawa but local police did not disclose further details, AFP reported.
'We Are Increasing Uniformed Patrols': Ottawa Police
"We are increasing uniformed patrols in the most affected areas of the city to ensure public safety and confidence," Ottawa police said in a tweet.
Hydro One, an electricity transmission and distribution utility in Canada, wrote, "We're responding to outages caused by severe thunderstorms moving across southwestern Ontario as quickly and safely as possible," noting substantial damage to transmission systems in Ottawa.
As many as 64 trucks were called in to cater to the regions that needed aid in Ottawa.
(With inputs from AFP.)
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