I think we get just under a month's worth of below -29'C weather here in Orillia each year. About a week of temperatures down to -40'C. During those days you can hear everyone's belt squealing in pain as they start up their cars.
I run 10,000-15,000 km intervals with the Petro Canada 0W-30, depending on the engine. That's roughly a year-long interval, although I could still see the dealership refusing to submit a warranty claim because you have 0W-30 in summer time - if they really wanted to squeeze every penny out of you.
Do you plan on keeping the vehicle long after the warranty expires? A synthetic 5W-30 should have no problems during winter; consider using one of those until the warranty expires, and then switch to 0W-30. Heck, I bet there are a lot of old-timer mechanics up here who still use 10W-40 in everything.
Personally, no warranty is going to tell me what to do with my car; I think I voided most of the Escape's warranty within the first two years. If they deny it, I'll just take it home and fix it cheaper and better than their techs would.
