Autumn is the prime time, specifically late September and October when the Agawa Canyon and the surrounding Algoma country turn. Book the Tour Train well in advance — it fills up weeks ahead during peak colour. Summers are pleasant and warm enough for the waterfront and outdoor activities, though bugs are a fact of Northern Ontario life in June and July.
Winter is cold (expect -20°C at times) and long, but not without appeal: the Bon Soo Winter Carnival in February is the largest in Ontario, and the Snow Train runs excursions into the canyon. Spring arrives late and is mostly mud season — not the most attractive time to visit.