What am I entitled to if my landlord doesn't fix a leaking ceiling (like there is a gaping hole)?

take pictures and break your lease sue from any water damage to your belongings

You are entitled to timely and effective repair by competent. If the problem poses a health risk, you MAY be entitled to cost for lodging until problem is fixed (this will vary depending on your locale and lease agreement). The landlord is entitled to reasonable access to your unit in order to inspect the problem and whatever is necessary to repair it. You are responsible for making it accessible and moving your goods out of the way so the workers can do their job.

You will need to check you ordances, etc in Montreal as they probably differ from those in the US. Usually you can fix yourself or have someone come in and fix it after a landlord ignores it and then deduct it from your rent. But check the landlord/tenant laws of you area first.

You will need a court order after informing LL and LL will have to pay for the repairs

You are entitled to move. He must be a real scum bag.