Denis, and Pratt, in rural Mexico on smaller roads, the vast majority of truck drivers are very courteous and careful around bicycles, much more so than here in Quebec.
Especially in rural areas, they are used to slow moving trucks, pickups, horses, people on foot etc.
The toll highways have more traffic, but generally have quite a wide shoulder, and so are pretty good to ride on, although noisey. Trucks do often straddle the wide shoulder to give more room for cars and other trucks to pass, so one must be careful.
I highly highly recommend using a good mirror while touring, this is indispensable.
Your route map idea shows you starting in a city on the east coast, but are you thinking of crossing the border at Texas and riding down through North East Mexico? I have a friend how lived in NE Mexico and described to me how bad it was for illegal activity. I also know a Mexican who actively discouraged me from riding in the north.
look up Crazy guy on a bike, you will be able to find trip journals , hopefully with some of the areas in the NE, and for sure, some from the Cancun area.