Iqaluit is an extreme Arctic destination and the season matters enormously.
Summer (June–August) is the obvious choice: temperatures reach 10–15°C, the sun barely sets for weeks around the solstice, the tundra is green and full of wildflowers, and hiking in Sylvia Grinnell is excellent. This is also when you're most likely to see beluga and bowhead whales in Frobisher Bay.
Late winter (March–April) has its own appeal: reliable dog-sledding and snowmobiling, the best light for photography as the sun returns after months of near-darkness, and average temperatures around -25°C that are cold but manageable with proper clothing. The sea ice is still solid and activities can venture further out.
Autumn (September–October) offers dramatic light and rapidly changing conditions — the first snowfalls arrive in September and the bay can freeze unpredictably. Spring (May) is the worst time: the ice is melting, the ground is muddy, and travel outside town is difficult.
Pack serious cold-weather gear at any time of year. Summer nights can still drop to freezing, and weather changes fast.