My Flat is within the city walls so the neighbourhood is too old to be designed for cars and there are very few homes with parking. Having said that you can unload a car outside the front of the building and there is several car parks within a 2 minutes walk, but they are 'short stay' and charge until 9pm. 

There is free on street parking outside of the town centre in the Wincheap area south west from the flat and about 5+ minutes walk away. Try Martyrs Field Road.

The city has 3 park and ride facilities, currently £4 per day but limited to 48hrs per visit. Google for Canterbury Park and Ride.

It depends what you want to do during your stay, many people who are just visiting