Just about everything in your statement is incorrect. For example, in TX if your Class A RV is over 26k pounds you need a MINIMUM of a Class B driver's license. If you pull a trailer and your combined weight is over 26k pounds you need a Class A driver's license (so everyone understands, a normal driver's license is a Class C ) and these can be either Commercial or non-Commercial but still need to be the correct CLASS AND if your vehicle meets the requirement of a Class A or Class B license and has air brakes then you need an Air Brake Endorsement on that license as well. Just because there are idiots out there driving large vehicles without the proper license doesn't mean they're doing it legally.Unbelievably no matter how big your RV is a regular private drivers license works in North America. I have a commercial drivers license since it’s required for my 12.7 metric ton U500 camper in Europe, Russia, Australia etc. But I have never been asked to show it anywhere.
To be perfectly clear: if it is an RV you do NOT need any special license in USA or Canada.
There are many huge RVs being driven by people that should not be driving a Prius.
As mentioned before, each state handles their internal licensing in a different manner but will honor every other states license as long as the holder is legal within their home state. I cannot verify but would guess that is similar in Country to Country issues as well. You might check with either the Mexican or US Consulates in your area to see if they can assist you.