We have 2-3 days in both Montreal and Quebec in August. Looking for favorite activities in both cities. We will do a walking tour of both cities. Museums ok but not big modern art people. Won't have a car in Montreal (except on our way out of town) but will in Quebec.

Thanks
MCHS

You won't need a car in Montreal which has an excellent public transportation system. There is another thread on Montreal going which has good suggestions for activities there.
Montreal in September
I am not sure where your walking tour will be but it can only cover a small part of the city (probably Old Montreal?), so check out other neighborhoods.