Canada’s climate is hugely varied, but it’s a safe generalization to say the areas near the coast have milder winters and cooler summers than the interior. July and August are reliably warm throughout the country, even in the far north, making these the busiest months to visit, with September also warm (and busy) in the south (note also that the sun sets much later in the far north in summer). In Newfoundland, the Maritime Provinces and the North the tourist infrastructure closes down completely from October to May, though the long autumn can be the best time to visit Ontario and Québec, when there are equable temperatures and few crowds. November to March is an ordeal of subzero temperatures almost everywhere except on the West Coast, though winter days in many areas are clear and dry, and all large Canadian towns are geared to the challenge of cold conditions, with covered walkways and indoor malls protecting their inhabitants from the worst of the weather.
The southwestern parts of British Columbia enjoy some of Canada’s best weather: the extremes are less marked and the overall temperatures generally milder than elsewhere. Much of the province, though, bears the brunt of Pacific depressions, so this is one of the country’s damper regions: visiting between late spring and early autumn offers the best chance of missing the rain.