You do not need an International Driving Permit.
From the FCO website on Canada with regards to road travel:-
"Road travel
Each province and territory has the authority to establish its own traffic and safety laws.
Seat belts are compulsory. Right turns on red lights are generally allowed, but at some junctions in towns and cities, you can only turn right on a green light. In some parts of Quebec, right turns on red lights are not allowed.
You can hire and drive a car in Canada using a full UK driving licence. You don’t need an International Driving Permit. Carry your licence with you at all times.
Take out full insurance cover if you hire a vehicle.
Obey speed limits and take extra care when travelling on country roads. Watch out for wild animals.
Winter driving conditions can be extreme. Monitor local news and weather broadcasts and take advice before driving in winter. Snow tyres are required in some provinces.
For detailed information on road conditions throughout Canada and safety tips, see the Government of Canada, the Canadian Automobile Association and the Travel Canada websites."