I was told that being in Quebec might raise questions with the officer reviewing the file and cause problems in the application. So, I added a letter of intent to my application, explaining when and why I plan to move and why I have not moved yet. I moved from Montreal to Toronto late December (just as I had indicated I would in my letter of intent) and updated my address, and no questions were asked. I don't know for sure, but I am not sure that would be the case if your address is still in Montreal at the time they go through your file. And if they ask for an interview or some explanation in writing, that will surely postpone the finalization of your file for some time, likely months. From what I see, whenever they ask you to send something extra, it can take them quite some time to reopen your file and review what you have sent.
Another point is that when you are sent a PR portal request, you will be asked to give a valid address for the mailing of your PR card. I am not sure what would happen if the address is still in Quebec. There is an "address review" stage, but I suppose that is probably for reviewing the validity of the address (no PO boxed for example) only.