The Employment Standards Act allows employees to take 3 unpaid days each year for personal illness, injury, or medical injury.  This has required doctors notes in the past, but the government is looking to changes this and is covered in the article below.

Ontario Government Announces Changes To Requirement For Medical Notes Under The Employment Standards Act, 2000

https://www.mondaq.com/canada/employee-rights-labour-relations/1462458/ontario-government-announces-changes-to-requirement-for-medical-notes-under-the-employment-standards-act-2000