Well, not to put a damper on what sounds a wonderful adventure…BUT…
I met some very adventurous people when I was traveling in South America who had, in fact, driven from Canada, through the U.S. into Mexico.
There intention was to drive right to the tip of South America. They were very savy and experienced travelers, had been many places, spoke fluent Spanish. They were three young men.
Unfortunately, shortly after stopping for gas, on a not very busy stretch of highway, a vehicle came up to overtake them only instead, ran them off the road. Two men, whom they had seen at the gas station, pulled guns on them, took their car and everything they owned.
When they finally made it back to the Policia, to report these events, they were met with the attitude, “Stupid foreigners, count yourself lucky you escaped with your lives”, they were then jailed for not having travel documents or ready cash for a bribe.
Yeah, they did work it out, got their travelers cheques replaced, passports reissued, money wired to them to pay the bribes to make the first two things possible, etc.
The most remarkable thing was not that they had continued on with their journey, (we met them in Bogota), but that they held no ill will toward Mexico. But, recognizing the danger they had made the rest of the journey on public transport.
You may want to think carefully about what you are proposing.