Montreal and Q' City are wonderful places to visit. We only did a couple of days in each which met our needs of solid 8am to 10pm days walking+++. To each their own but research heavily on what you want to see and do in each location, and decide on how long YOU need based on your personality and way of travelling/touring/what interests you.
PS: As newbies at the time we made the mistake of driving our 36ft RV right down into town (think cobbled areas), and even entering into a carpark down there to finally get back out. Takes a lot to phase hubby driving this beast, but sure explained the odd looks folks were giving us within 30 secs of where we realized we shouldn't be in such a beast LOL. We don't toad so only bike/walk at our interest spots and thus far has worked well for us over many years.