Do I need to get an international licence to rent a car in the UK?
There should be no problems. I have a Bulgarian driving license and last year I rented a car in the UK without any problems. From Sixt General Terms and Conditions :
Conditions for vehicle use:
The vehicle must only be driven by an approved driver in compliance with the preconditions stated in the Sixt Rental Information of the United Kingdom / clause 1.The minimum rental age is 21 (twenty-one) years old. A young driver Surcharge will apply for a driver under 23 (twenty-three) years old. Anyone driving the vehicle must have a full driving license that is valid in the European Economic Area for the type of vehicle you are renting.
As DJClayworth already mentioned in his answer, you can use your Canadian driving license for 12 months.
No, you don't. This tool will tell you what license you need to drive in the UK. With a license from a Canadian province you can drive for 12 months as a non-resident, and can rent a car provided you satisfy the other requirements.
I would be on the safe side and get an international drivers license. In Alberta, Canada they're only about $40 (CAD) and take less then 20 minutes for them to issue. I assume your going to be renting a car? If so, I recommend paying the extra money to get a zero deductible insurance. We got lost in Spain on some back road, went to turn around and backed up into a sign causing the whole back window to shatter. When we took it back to the car rental place (I can't remember who we rented from), they didn't say a thing and we didn't have to pay anything extra for it. A GPS can also come handy if your not familiar with the area and some of the car rental places charge the same amount you would to buy a GPS then to rent it from them. So your better to buy one here in Canada (make sure you load the England maps onto it) and pack it in your suitcase.