ON Canada - you need to get a discharge statement from the bank to show that your mortgage is fully paid, Normally the bank will charge you a fee to get this. It is your responsibility to have the discharge registered against the title of the property so the lien is deleted from your record. Then you can ask the registry office if you can get a copy of the title for your use.

A pre approval means that the bank will issue you a mortgage loan based on the information provided however before approving the mortgage the bank will verify the documents. If the documents were not verified and you already got fired then most likely you will not be able to get approved as the x employer will not verify the information of your employment.