The Tolt Pipeline is not paved. The hills are rather steep, exceeding 20% grade in places. I ride it on my Mountain Bike for a good workout, although there is no reason you could not ride it on a cross bike with cross tires.
Marymoor to the Samamish River Trail to the Burke Gilman Trail is marked and easy. Burke Gilman is closed in Lake Forest Park, a detour is provided but I have never used it.