I have a flight from Istanbul to Vancouver with long overnight layover at Montreal. Where do I need to do my quarantine if I decide to spend night at hotel? Or can I stay at the airport for a night to wait for my flight? Keeping in mind the covid situation
The High Commission of Canada in India has perhaps the most unambigous wording from a direct official source https://www.facebook.com/notes/canada-in-india-high-commission-of-canada/frequently-asked-questions-travel-to-canada/3287653284620616/:
Do I need to self-isolate immediately at the first port of entry in Canada?
If you are arriving from outside Canada and are deemed safe to fly, you may board a connecting flight to your destination. However, upon arrival at your final destination, you must go directly to the place where you will isolate, and remain there for 14 days.
An article from the CBC concurs https://www.cbc.ca/news/politics/mandatory-quarantine-hajdu-1.5509508
A health official later clarified that only people with symptoms will be quarantined in the city of arrival and that travellers without symptoms can continue on and isolate at their homes.
In general, note
The emergency orders under the Quarantine Act do not allow people to travel to Canada for optional or discretionary reasons, such as for tourism, recreation or entertainment.
Further, I called CBSA who declined authority in the question and then the COVID-19 Information Service at 1-833-784-4397 and they said about this specific situation she has the right to overnight in Montreal and can continue to Vancouver. I still would strongly recommend to call the airline as well.