Let's start with Ottawa where I spent many years of my life.
Ottawa has lost some of its best retaurants in the last 5 years. Though many new ones have cropped up, the quality is not what it was. You'll find that you'll get a much better meal outside of the city, either in Hull or in Gatineau, which is about 15-20 minutes from the city by car.
Hull used to be the scuzy spot accross the bridge where all the kids went to party because Hull is in Quebec, which means bars close later and the drinking age is 18 (as opposed to 19 in Ontario). They have recently harmonised with Ottawa, so all the clubs have shut down and are slowly making way for a nice little restaurant community.
Still, the best places are in the Gatineau hills(it's also very beautiful!). The one that I recommend is L'Orée du Bois in Chelsea. Very French, cozy, a romantic little cottage; it's the only place in the region where you can get good (really good)sweetbreads. Call ahead to make sure they have it on the menu that night. If it's not, they might put it on the specials for you as they have for me inthe past. The owners, a couple, are great. Another good place is Les Fougères. They seem to be getting more press but I prefer L'Orée du Bois hands down.
Restaurant l'Orée du Bois, Kingsmere Road, Old Chelsea, (819) 827-0332
Les Fougères: http://www.fougeres.com/welcome.htm