https://www.ontario.ca/laws/statute/01m25#BK58
Sidewalks
(9) Except in case of gross negligence, a municipality is not liable for a personal injury caused by snow or ice on a sidewalk. 2001, c. 25, s. 44 (9).
Notice
(10) No action shall be brought for the recovery of damages under subsection (2) unless, within 10 days after the occurrence of the injury, written notice of the claim and of the injury complained of, including the date, time and location of the occurrence, has been served upon or sent by registered mail to,
(a) the clerk of the municipality; or
(b) if the claim is against two or more municipalities jointly responsible for the repair of the highway or bridge, the clerk of each of the municipalities. 2001, c. 25, s. 44 (10); 2017, c. 10, Sched. 1, s. 4.
Exception
(11) Failure to give notice is not a bar to the action in the case of the death of the injured person as a result of the injury. 2001, c. 25, s. 44 (11).
Same
(12) Failure to give notice or insufficiency of the notice is not a bar to the action if a judge finds that there is reasonable excuse for the want or the insufficiency of the notice and that the municipality is not prejudiced in its defence. 2002, c. 24, Sched. B, s. 42.