Is this held personally ?
If so, there are two issues here to be aware of
A) what is an eligible expense: you can deduct ALL expenses related to your business, incl. interest on loans. The issue is if this loan exceeds the acquisition price many years ago minus accumulated depreciation plus enhancements if not invested.
B) when to pay taxes: on sale usually.
Example: you buy for $200,000 with a mortgage of $160,000 and now asset is worth $300,000. Mortgage has been paid down to $130,000 and you depreciate asset $25,000 (CCA) and you added $10,000 in improvements. Your new mortgage cannot exceed $200,000 + $10,000 - $25,000 = $185,000 to allow all interest to be deductible UNLESS you buy another asset for income purposes, say another rental property. If you buy a boat or a new BMW then they could argue that this loan's interest is not deductible in full. [ But that is rarely enforced by CRA but certainly they could ]