Certainly not out of the question. Most attractions are still there, minus the fall colour, a little less green, add some white esp in the morning. You can see steam coming out of every mouth, perhaps from manhole covers too. A lot more people in Montreal will use the underground tunnels and mall. The snow birds will be going or gone south already. If it does snow, it may be slushy in the afternoon. You'll find all the eateries cozier, walking pace a little faster, and more people oriented towards hockey. The river and waterfalls won't be frozen as yet. The ambience and the people are still there. French is still in use (with quebec accent).

Yes, go for it.

it will be cool but if you want to leave the sun go for it! Bring some thick sweaters!

Sure, why not. Weather is only one component of a good vacation. You will miss out on the beautiful fall colours, and it'll be a little grey and dreary out, but you can still enjoy a nice vacation in two great cities.

I'm sure you'll enjoy the good food and different culture that we have to offer...

have fun,

rob