As far as I know:
At just under 10% to the minimum 5% down payment the CMHC or Genworth mortgage insurance premium is 2.75% of the mortgage amount. That premium is one-time, and can be added to the total mortgage loan and amortized.
From just under 15% to a 10% down payment the premium is 2%.
From just under 20% to a 15% down payment the premium is 1.75%.
Remember, this kind of mortgage insurance protects only the lender if you default on your mortgage. You get nothing from this insurance in case of default. If you want to be protected yourself get separate life and disability mortgage insurance. (And even that won't protect you in case of an ordinary default.)
Also keep in mind that the percentages involved are based on the appraised value of the property, which is not always as high as the purchase price. A low appraisal can cause problems as it can significantly reduce the total amount of the mortgage loan that will be approved for a property.
Another point: the maximum amortization period for a "high-ratio insured" (less than 20% down) mortgage is 25 years.
My advice: Talk to a licensed Ontario Mortgage Agent or Broker, who will generally be more than happy to give you lots of free advice about the many variables involved in mortgage financing.
And it's true: fixed mortgage rates have never been lower!
As mentioned in The Star business section today, with the negligible spread between the best variable mortgage interest rates and the best fixed 5 year term closed rates today, hardly anybody is choosing to go with variable rates. One uptick in the Prime Rate and and the variable rate advantage will be lost. (That is, unless you believe that interest rates in Canada will fall even farther in the next 5 years.)