Canada's size means there is no single answer — the country spans six time zones and climates ranging from temperate rainforest to arctic tundra. That said, most visitors come in summer for good reason.
Summer (June–August)
The most popular season, and for good reason. Days are long, national parks are open, festivals fill city calendars, and the west coast is at its best. July and August are peak season; expect higher prices and advance bookings required for popular parks like Banff and Jasper. The Maritimes and Québec come alive in summer. In the far north, June and July bring near-continuous daylight — bizarre and beautiful.
Downside: crowds and prices. Book accommodation well ahead, particularly in the Rockies.
Autumn (September–October)
Arguably the best time to visit eastern Canada. The fall foliage in Québec, Ontario, and the Maritimes is spectacular — typically mid-September in the north, running to late October further south. Fewer crowds than summer, and temperatures are still pleasant. In the west, September is still warm and sunny in BC.
Winter (November–March)
Canada is serious about winter sports. Whistler–Blackcomb (BC), Banff Sunshine and Lake Louise (Alberta), Tremblant (Québec), and dozens of other resorts draw skiers from around the world. Cities like Québec City and Ottawa have winter festivals worth seeking out — Québec's Winter Carnival and Ottawa's Winterlude are highlights. Montréal, Toronto, and Vancouver have lively indoor cultural scenes that make them fine winter destinations.
Winters are genuinely cold in most of the country. Prairie temperatures can drop to -30°C (-22°F) or lower. Pack accordingly, and layer up. Vancouver is the exception — mild, rainy winters but rarely freezing.
Spring (April–May)
A shoulder season. Mud season in many areas, lingering snow in the mountains, and unpredictable weather. But there are advantages: whale watching off the BC coast starts in spring, wildflowers appear in the southern Rockies, and prices are lower. Québec's maple syrup season runs February through April — a good reason to visit the province then.