Of course, DR Jennifer and DR Michael Shayne are our resident experts on the weather in Canada, but I've been to both Ottawa and Montreal in summer (July) and experienced 70s and low 80s. It was starting to cool in September, whereas in DC September is still hot, so a shorter summer than DC, but still quite ample, to my mind. But I don't like hot weather. And I'm told that British Columbia is quite temperate.