Autoroutes, or limited-access highways, such as the 20/40/55 or any *40, *20, etc. are considered freeways. This are drawn in yellow with a red outline on the province's official road map.
An exception to this rule is Rte 125 between Aut 440 and the Island of Montreal, which is a freeway in all but name. Aut 50 is also still a freeway, even though some small parts of it are not limited access and some are only two lane with no divider. Aut 20 is not a freeway in Vaudreuil-Dorion because there are traffic lights on it there.
Major highways are shown in red on the official map.
Minor highways are shown in orange on the official maps.
A very general rule of thumb is that 100-series highways are major while 200 and 300-series highways are minor. This is not completely accurate, however, so look at the road map.
Please consult this official map of Quebec to determine the status of non-highway roads.
Of course, the Montreal area is distinct. You may read more detail on the Montreal Area page.