Can they deny an existing homeowner a mortgage? In the US, getting a mortgage is often a convoluted process that takes weeks of effort to put together and can fall apart at any time.
The truly terrifying thing is that the banks have been adding clauses to the mortgages that on renewal if the market value drops below the outstanding balance, the homeowner is required to pay the difference in order to renew.
This is scary because they will not have paid off much in the first 5 years, but the house price can certainly drop a lot in 5 years in a down market, and there would be very little hope for finding a new lender willing to offer a new mortgage for more than the market value of the house.
Getting a mortgage in Canada is (in my experience) a very weird process for an agreement over such a large sum, but typically can happen within a week.