Every November, as soon as the month jumps in, I have this feeling that "I should, but I shouldn't switch to winter tires." The fact is that, even after waking up every morning with 0 to 4 degrees Celsius and having all-season tires, it is hard to guess when would be the right moment to do it.
November or December?
I remember that, three years ago, the first snowfall (that stayed) in Montreal was on December 29th. It was a huge one, about 75cm, but it is not the regular time of the year. The year after, it was on late November. Last year, early December. Is there a pattern? Hell no, but there is one thing you must avoid, for sure: the day after the first snowfall, you won't find a tire change appointment for, at least, two weeks.
What I always do, is scheduling the change to be done between Nov 20th and 30th. It is a guarantee of nothing, but at least is the average moment where it should be fine to extend the life of my winter tires for up to 5 years or more. Even by having availability earlier, I always do it on those dates to make it "the closest" to the average as possible.
I'm using as a reference, the city where I live, but t varies depending on where in Canada are you located. I would speculate that for Calgary/Edmonton, a good moment would be early November and the same for Saskatoon & Winnipeg. Atlantic Canada, GTA and southern Ontario & Quebec, late November.
Where to Do It?
Well, if you don't have winter tires yet, I encourage you to go and see the availability in the nearest Canadian Tire. Although there are many other places where you can find these, the availability, variety, and quality of their stock is good enough for most people.
Now, regarding the installation, you have tons of options. You can do it either there or at any local workshop. But the most important thing today: schedule your appointment. These won't be around for a long time after the first snowfall. And remember: no matter what, winter is coming.