Just as the Victoria Day (in Canada) / Memorial Day (in US) weekends are the (unofficial) start of summer, the Labour Day weekend is the unofficial end of summer. By the beginning of September, everyone is back in school, and during the week, business is dead. Most of the hotels have unbelievable rates for Sunday to Thursday stays, with higher rates on the weekend.
Many of the souvenir shops have sales as well to try to clear out inventory.