Your American or Canadian automobile insurance is not valid once you cross the border into Mexico and you can be cited for failure to have insurance by Mexican law enforcement authorities. Worse still, if you have an accident while in Mexico, even if you were not at fault, you can be put into jail for failure to have liability insurance coverage. It's not something to relish and should be avoided at all costs.
Tourists travelling in Mexico who have wrecks can find themselves in jail for even a mild fender-bender. They are civilly responsible for any damage they might cause...even to trees or rocks along the roadside. Harming a person is even more of a problem and without insurance you have a major problem with the policia. An insurance policy and the claims person from that insurance company can make this problem much less severe.
Your present insurance might pay to replace or repair your car, but you must get it back to the U.S. to get that taken care of. The liability coverage you now have will not be recognized within Mexico.
BTW: The border crossing in the deep South of Texas at Progreso is a very busy crossing for foot traffic, but is rarely congested for vehicular traffic. If your plans take you to the Northeastern corner of Mexico, it's a great place to cross.
