Rosanna's flat is a perfect place for a couple to enjoy Venice. It is away from the madness of St Marco's square and in a quiet neighborhood. The garden in the back is perfect for relaxing with some wine at the end of the day.
There are quite a few good restaurants in Canneregio but you need to get lost to find them. And a tip for people who have never been to Venice before, however long Google Maps says it will take for you to walk somewhere, double it at least. You will do alot of walking in Venice but i really can't think of a better city to walk around.