I live in Ontario so this explains our provincial holiday and below that is more info regarding the holiday across Canada.
"Do you know why the first Monday of August is a holiday in Ontario? If you answered no, you're not alone. Most people simply associate it with having an extra day away from the office.
And although that alone could be enough of a reason to celebrate, the true meaning behind the holiday is to honour John Graves Simcoe, the first Lieutenant Governor of Ontario (then known as Upper Canada). He was also the founder of the Historic Fort York, the birthplace of modern Toronto. "
Many Canadian provinces and territories have a civic holiday to celebrate some aspect of their culture or history on the first Monday of August.
The first Monday of August is a holiday for people in many parts of Canada. It is a statutory holiday in some provinces and territories but in others it has another legal status. It is often called the "August Holiday", "Civic Holiday", "Provincial Day", or other local names.