Mount Royal - go up Pine Ave and enter the park. Then follow the gravel path - it's a great jog up and down. There are some trails that follow the edge of the south cliff but the signs are poor so bring a mapping gps. There is a long stairway from below the park to the top. The northern part of the is summit covered with playing fields and picnic areas. You can go east as far as Pine Avenue. Great views at the top but not much of a hike if you're serious.
Ottawa - Gatineau Park has trails but no great hikes - lots to see. The trails along the river are discontinuous.
Toronto - there are pleasant ravine trails and the lakeshore has a paved path. The main hiking trail is the Bruce Trail, which has some interesting sections in the Mount Nemo, Blue Mountain and Bruce Peninsula areas. Hiking the section along Georgian Bay from Lion's Head to Cypress Lake is unique and worth the trip (four hours from Toronto). The Bruce Trail Guide provides complete details. The hikes in Algonquin Park, three hours north, are limited but the Centennial Ridges Trail is the best in the park for a day trip and there is a long Highlands backpacking trail. But trust me, rent a canoe and see it from the water - it's special. Canoe Lake on Highway 60 is the place where most people start and there are rentals. Other interesting half day hikes are at Torrance Barrens and Hardy Lake near Bala (two hours from Toronto). You can get a pretty good idea of any of this stuff on Google Earth. I'd be glad to continue with posts or PM me.
Great add'l info...thanks. I continue to lean toward Montreal because of the urban tourism opp'ys we will have during 2 days we would spend there if we choose the Montreal/Laurentians option. My last visit to Montreal was 20 years ago in '88, and I definitely didn't do it justice on that visit at all. Not concerned about the "not serious hike" aspect of Mont Royal at all...a "mellower" hike there would suit me/us perfectly. The "more serious" day hike is for once we head away from the city.