Frankly I think we need some frontier outlands to exile all of the terrible people to. Militarized hard borders North and South. We could steamroll the Canadians and let the few good ones move south. The human detritus that doesn't freeze can try establishing their own society and eventually states up there. The Canadians not good enough for US entry but unhappy with the arrangement can be expelled into Mexico. If they cause too many problems with it we have a sit-down with the relevant cartel bosses and do a little regime change. They use their scary violence to keep shit somewhat normalized.
In return we federally un-schedule MJ, limit LE action to north of the border, and for simplifying management we'll go ahead and assume control of everything north of the Darien Gap. US gets the Panama Canal and a zone immediately around it to establish a military presence. That way the cartels will know the full might of the US MIC is ready to sandwich their ass if they get too cheeky. Helps minimize the riff raff moving north as well.