Winnipeg has a more extreme climate than Montréal. Here we have a large temperature range. It gets really hot in summer and really cold in winter. I prepped and had my pad poured for my garage. Six years later still not a single crack. I'll sum up how I did it.
First, I went to the city to get a pamphlet on what is code. Here, a garage can take up no more than 19% of total lot space. So I went max
(20x26) and I will say I still didn't have enough room. So if you're planning on tinkering later, I suggest you go a little larger than just enough for your car. You might want to consider planning for some room on the side for a bench/work table and a tool box.
Code here required that the pad be one foot thick on the perimeter of the pad, and then six inches in the middle. I considered drainage from my yard and my neighbour's yard. I wanted my pad to be elevated so that it would not get swamped in the spring.
Bobcat came to take away some dirt.
I got some 2x6 forms from my contractor friend who would eventually do the pour. Used a sledgehammer to drive down some 2x4 spikes to which we would hammer the forms.
To make sure the forms were level, I borrowed my friend's laser level. This consists a of tripod with a rotating laser head. This head must be perfectly level. The other part of this tool is a pole to which a laser detector is attached. When the laser hit the detector directly at the proper elevation, it would beep. I did this for the entire perimeter and adjusted the forms until the forms were level all around.
Had a load of 3/4 down delivered.
Spread the gravel with a shovel to end up with the form that would result in the desired thickness of the pad. I should add that the one foot depth on the perimeter was about a foot and a half wide before building it up in the center.
Rented a compacting machine. The one that vibrates. I went ape on this. Overkill even. I compacted for an hour and a half or more. I believe this is why I had no cracks later.
Put down poly, laid the rebar, tied it with wire, supported it with broken pieces of sidewalk pad.
Then it's time for the pour. I suggest you get a pro to do the pour and a few friends with shovels. My contractor friend guided the pour. Cement truck came and we spread the concrete to each corner.
The pro can finish the surface with a smoothing tool. Looks like a rake but at the end of the handle, its a flat piece of wood. I wanted an extra smooth finish so we rented a power trowel. We made a night out of it. Every hour and a half he would trowel the surface, all the way to four in the morning. Everyone sat around the fire and once in a while my friend would fire up the trowel for another polishing. I had really good neighbours.
I hope this gives you and idea of what's involved in this job.