As per our article https://turbotax.intuit.ca/tips/tips-for-renting-out-your-house-6375

"Unlike U.S. citizens, Canadians can’t normally deduct mortgage interest paid on their principal residence. The only exception is when you rent out part of your home. So if you have a mortgage, you can claim a portion of the interest as a tax deduction. For example, if you rent out 40 percent of your home, you can claim a tax deduction for 40 percent of your mortgage interest you paid in the year."

Hope this helps.