It is depend where would you start and end the trip and how many days , this is what I'm planning for my Canada trip.( travel by car) there are many car rental company provide cheap rate per week.
Start from Toronto-Ottawa- Quebec-Montreal.
Below are the places to visit.
Toronto- CN Tower-world tallest tower.
Ottawa - about 5 hours dive from Toronto. Parliament Hill is the place must see both in day and night. Sound and light show is at night, shows Canadian history and culture.
Quebec-from Ottawa to Quebec 5 hours drive.
-Saint-Laurent,Terrase Dufferin
Montreal-Basilique Notre-Dame De Montreal,Notre-Dame-de-Bonsecours and shopping on Catherine street.

Never been there yet, I'm in step of searching details as well.