The official name for this holiday varies between the provinces and even between municipalities. Here in Ottawa it's just called "the August long weekend". Mighty original, but nobody complains because it's a paid holiday ;)
In parts of Canada, the term "Civic Holiday" is a generic name referring to the annual holiday on the first Monday of August. However, this definition is far from uniform nationwide as two provinces and one territory do not recognize it at all, and five other provinces do not oblige employers to offer holiday pay on this day, thus making it a civic holiday in the legal sense.