in ottawa, (beautiful beautiful city, and no i am not biased) ;o)
downtown you have the parliament buildings, with the changing of the guard (quite a site!) it is a big thing every day at i believe 10am on the hill. there are tours inside parliament, and you can walk around (the cat guy in behind!)
from the hill you are a hop skip and a jump away from chateau laurier (a hotel which some say is an attraction in itself) the locks between the two (amazing photo spot for the canal) the Rideau Centre (shopping mall) the NAC (national arts centre) the By Ward market, lots of restaurants, the National Art Gallery, War Museum, Museum of Man (in hull, quebec ...just over the bridge) If you go in the spring (May) you would take advanage of wonderful spring weather with the tulips in full bloom (and the tulip festival). Downtown you also find boat tours on the Rideau Canal (and if in the winter, you can skate on it..longest skating rink in the world! ) Ottawa has beaver tails for snacks, sparks street (a pedestrian street with stores, considered an outside mall) Oh I could go on. :O) You can get passes to hop on and off the 'double decker' busses that go around the downtown core and the touristy areas.
Hope that helps a bit!