The suite's legal status is what decides whether the strategy works. An egress window, a separate entrance in many cases, proper fire separation and a permit on file are what a lender and an appraiser check, and an unpermitted suite can add close to zero toward qualifying even if it is fully finished.
On the money side, CMHC's lending guidelines cap housing costs at roughly 39 percent of gross income and total debt at 44 percent, and a portion of a legal suite's rent can be credited toward those ratios, which is the actual mechanism behind the mortgage helper.
Get the suite legal first, then the financing math and the rental income both work the way house hacking promises. Get your hand-reviewed valuation from Joel Dyck.