Tea at the Chateau Frontenac is quite an experience! If you reserve on certain days, you will be joined by a "hotel guest" from the early days of the hotel, who will tell stories of the grand balls and high life of the 1800s.
The things to see are the old city itself, both levels of it, which are connected by a funicular. At its foot, the entire street is dedicated to shops of Canadian craftsmen's and artists' work. The market, near the river, has products from local farms and food producers, from emu oil for your complexion to artesanal cheeses and chocolates with maple cream centers. The art museum is excellent, and historic sites all over town are beginning their special exhibitions honoring the city's 400th anniversary in 2008.
Be sure to see Montmorency Falls, just outside of the city. It is higher than Niagara -- an entire river drops off a cliff and into the St Lawrence.