On I-90 through Cleveland, there’s a large number of 18-wheelers from Canada. Almost all of them are from trucking firms based in Quebec. None from Ontario or any other provinces: just Quebec. Is Quebec the trucking capital of Canada, and if so, why?
To the contrary, this report, prepared in 2003 for the Canadian government, indicates that Quebec has a lower number of registered trucks than their population would suggest (if distribution was equal per capita). It’s more likely that you are seeing a high percentage of Quebec-plated trucks because you are on a corridor that a particular industry is using. In particular, Quebec exports transportation equipment (automotive, airplanes, etc.), primary metals, pulp & paper, electronics and lumber (distinct from paper products).
On the Maine Turnpike, I see a lot more trucks from New Brunswick (mainly Sunburys) than from any other province, but Quebec is second.