I am from Ottawa

and I would say that Montreal and Quebec City have more to see so if you wanted longer stays I would say in those two cities. Not that Ottawa isnt great but its a smaller city. To give you an idea of driving distance, Ottawa is about 1.5-2 hrs from Montreal (depending on speed and traffic) and Quebec City is about 5 hours from Ottawa.
Montreal traffic is BRUTAL. For some reason there is only ONE hwy through the city so always try to avoid traveling through rush hour.
Now for things to do!
Ottawa
Parliament Hill-is a must see. Tours are free
http://www.parl.gc.ca/visitors/index-e.asp and is beautiful!! Walking around the grounds are also great.
Cats on Parliament Hill-keep there is a CAT sanctuary to the side. A hidden gem but super cute and a must see!
http://www.parliamenthill.gc.ca/histoire-history/terrains-grounds/snctr-snctry-eng.html
The Byward Market is really great-lots of cute shops and stalls. You can walk to the Market from Parliament Hill and see the Chateau Laurier-a mini version is in the Canada Pavilion. In the Market is where you can get Beaver Tails-yep, the original location. Along your walk you will also see the rideau canal and there are boat cruises-pretty cheap. Take the one along the Ottawa river-the sunset cruise is my suggestion.
There are also tons of Museums in Ottawa.
Montreal
Its a huge cosmo city. And GREAT for shopping. Here is what I would recommend:
Walk up to St Catherines street for great shopping
Seeing the Old Port area-so gorgeous and great restaurants
Want to try good smoke meat? There is a famous restaurant and its called Schwartz's you may have to wait in line but worth it!
http://www.schwartzsdeli.com/
The Ottawa Bio Dome. Former Olympic building is now a indoor type zoo where you can see all the worlds biodiversity.
http://www2.ville.montreal.qc.ca/biodome/site/site.php?langue=en
Mont Royal for a great view!
Notre Dame is a great church to view!!
Quebec City-my favorite city

and I will be doing a "mini moon" there after my wedding. Just SO SO gorgeous. I would recommend staying within the city walls in the old part of the best experience. My top two hotel recommendations are: Obviously Chateau Frontenac if you have the cash for even one night!! OR even going there for a dinner or the BEST BB in town (ask to stay in the top loft) and former house of a solider on the Plains of Abraham-Maison Historique of James Thompson
http://www.bedandbreakfastquebec.com/ The BEST place to stay. Very affordable, gorgeous historic house, great owners. Not to disappoint.
Best upscale restaurant is Le Saint Amour. A bit pricey but so so worth it. Still the best dinner there
http://www.saint-amour.com/
The Haunted Walk of Quebec City is really cool and great!! Always a must do.
Best walking tour with food:
http://www.toursvoirquebec.com/en/home BEST Tour guide in the CITY! I have been back more than once! Any of them are great.
I know lots of restaurants in each city so send me a message if you want to know more
