I also recommend taking the metro (subway), especially the blue line. Most stations are very well designed and look like an art gallery or museum. I have visited all the stations in the network.

I also enjoy walking around the small towns in Québec as most of them give a very different vibe from the typical towns in rest of the Canada. Lots of churches and heritage buildings, and they are well decorated around Xmas. A few of them are a short drive away and can be reached by public transit.