In this article, we estimate the determinants of hours of work for Ontario and Quebec using Statistics Canada Labour Force Surveys. We first illustrate that intensity – hours worked per employed person - has decreased in Quebec relative to Ontario between 1997 and 2005. We then proceed to show that differences in average observed characteristics between the two provinces explain at most 10 % of the difference. We next analyze in more details the impact of industry, occupation, public sector status and union status on the distribution of hours of work. We find that if the size and distribution of unions in Quebec were the same as in Ontario, the proportion of workers in Quebec working reduced hours would decrease significantly while the proportions working long or very long hours would increase.