The problem with labour day weekend is that a lot of the campgrounds will be full or nearly full as most Camper People in Canada go out for the last long weekend of the camping season. The other issue with labour day weekend is that a lot of the provincial and National park campgrounds close for the winter just after the weekend. However these campgrounds are mostly in the interior on BC and the mountainous areas. Vancouver area and Vancouver island as well as the Okanogan Valley are the some of the areas that will see the campgrounds stay open longer.
I want to stress that not all campgrounds will close, most privately owned campgrounds are still open, it's mostly the ones in the provincial and national parks.
I would recommend making reservations for labour day weekend and do it now. After that weekend reservations usually are not required however it really depends where you are staying and if you want to ensure that beautiful lake side site etc.
Soup.