Fall colour on Cape Breton is not a subtle thing. The Highlands turn fast — maples go full red and orange in the last week of September, and by the first ten days of October the Cabot Trail is running at its visual peak. What makes this different from, say, a New England colour drive is the scale and the isolation: the plateau drops straight into the Gulf of St. Lawrence, so you get ridge-top colour and open ocean in the same frame. There is no equivalent of that in eastern Canada at this time of year.
The honest trade-off is weather. Temperatures in October sit between 10 and 18°C during the day and drop sharply at night. Rain is common, fog rolls in off the Atlantic without warning, and a clear morning can become a grey afternoon before lunch. That is not a reason to stay home — the light after a rain squall on the Highlands is frequently spectacular — but it does mean packing a proper rain jacket and accepting that one of your driving days might be socked in. Build a flexible itinerary.
Celtic Colours International Festival runs for nine days in mid-October and changes the character of the island dramatically. Venues across Cape Breton — from church halls in Mabou to the Strathspey Performing Arts Centre in Baddeck — host Celtic musicians from Scotland, Ireland, Brittany, and the island itself. Accommodation fills up weeks in advance during the festival. If you are not planning around Celtic Colours, late September and the first days of October offer the same colour with far fewer cars on the Cabot Trail.
Most of what you want to do is still open: Highlands National Park, the majority of Cabot Trail restaurants, whale-watch operators in Chéticamp, and the main cultural sites. A handful of smaller seasonal businesses begin winding down by mid-October. This page covers the specifics — what is running, where to base yourself, and how long to plan for.