The one consideration for legalizing weed to deal with the cartels is that they still make a majority of their money off the weed. If you legalized weed they would still smuggle coke, heroin, meth (remember when that was made in America?), and people. My guess is that they would make up the difference by fighting over territory and taking over all human smuggling. Depending on how bad the new immigration bill is, that might be a huge business opportunity for them. Controlling routes, coyotes and even the issue of ag worker visas on the Mexican side.
Cartels already control the human smuggling on this border. Cartels are pretty diversified, if they ever joined forces instead of fighting each other they would likely control whatever they wanted to- even here.