Mathieu and Maude's place was a very enjoyable stay overall. Parking on the first night was a bit tricky because there is limited free parking on their street, but after 9pm on the Friday the whole street became free so it wasn't a problem. Sadly we didn't get to meet Mathieu and Maude, however we were greeted by Maude's dad who was very hospitable and kind.
The apartment itself is as described; a basement studio apartment with a pull out sofa. Clean, easily accessible and in a quiet location. However, as a basement apartment we found it to feel a bit damp; for example the towels and bed sheets although clean had a damp smell. Also it is not well soundproofed, meaning that when we were very tired on our first night, we found it difficult to drown out the noise of the apartment above it. Sadly there is nothing that can be done about this and it didn't diminish our satisfaction with our stay.
To get to the main attractions of Quebec City, it is maybe about 40-45 minutes to walk. However the walk passes by some pretty major roads so I can't say that it is the most beautiful walk. But the city itself is so beautiful and I feel we were blessed with the weather, especially given that the summer in Canada so far this year has been so temperamental. All in all it made for a wonderful stay.
My only negative is that having stayed in a 2 bedroom apartment which was only a 10 minute walk to the old city which was less expensive than Mathieu and Maude's place, we found it to be expensive for what it is. Otherwise perfect all around :)