Most recreational vehicle owners traveling or living in Mexico are Canadian. I suspect that most of our Mexico forum contributors are/were also Canadian. It's pretty obvious.
I would be willing to stick my neck out and at least here in southern Mexico and say that there are at least at many as, if not more RVer's from the US here.
There sure will not be many Canadians as we cannot cross into the USA. However in normal times Canadians would probably be 50 % of RV travelers in Mexico
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I always heard it was closer to 80%. When we traveled around all our campground mates were Canadian. Sure a lot of Mexico plated cars & pickups north and southbound on I19 in Arizona. (road between Nogales & Tucson) Does not seem much of a slow down of crossings here. Friends who have walked across said it took at least 1 1/2 hours to cross back North into AZ.
There was a tidal change in the early 2000's - not sure if it was September 11 or the dot.com implosion. Our financial situation changed to the point we could not afford to go for 6 years. When we returned the landscape had changed. I'm basing this on observations in Sinaloa and the GDL area. Anyhow, folks from the United States are definitely missing incredible experiences by avoiding Mexico. College students and cruise boat passengers may very well be mostly from the US.
In this forum there are remarks about the United States that have a pronounced Canadian perspective. That's all I have to say about that.