Daylight hours are the general factor when it comes to leaves staying on trees, but it depends on the variety of tree, and the weather of a given year. Calgary is probably an outlier compared to most places as the fall weather can have drastic dips some years. It also depends on the variety of tree, for example Amsterdam is a bit further north than Calgary, and many of their trees do lose leaves earlier than Calgary, despite being in a more temperate climate. I'm guessing there are some shrubs in Amsterdam that are still green in the December due to the temperate climate (like one would see in Vancouver). There are also other factors, trees also grow slower in general due to cooler overnight temps compared to other places. The freeze/thaw cycle is hard on almost all trees.
Different factors for different varieties but the point being if trees get decent water they can grow here despite early frosts or other challenges.