Going with the minimum has a real cost: the insurance premium is added to your mortgage and paid down over the life of the loan, plus PST on that premium collected upfront at closing, so a smaller down payment means paying interest on a slightly larger loan for years. It is not free money, it is deferred cost.
Twenty percent down avoids CMHC-style mortgage insurance entirely and gives a lower monthly payment on the same purchase price, but it also ties up more of your savings in the property rather than keeping it liquid. Which side makes sense depends on your other debt, your income stability and how the minimum down payment on a home near the current benchmark price, currently $22,235, compares to what you actually have on hand.
There is no rule requiring 20 percent, only a set of tradeoffs between insurance cost, monthly payment and how much cash you keep in reserve. Get your hand-reviewed valuation from Joel Dyck.