If I lived on the Canadian border and smoked, that'd be an interesting answer. But, to your point, there is a pretty lucrative black market from Canada and Mexico for liquor, smokes, and prescription drugs.
That's why I advocate simply decriminalizing drugs. No taxes, no laws, no regulation. If you want to grow it, make it, sell it, buy it, smoke it, shoot it, share it with your friends and strangers...go for it.
There are plenty of criminal laws against most of the illegal activities in which people might engage to pursue a non-criminal drug enterprise. If you worried about self-destructive behaviors and health issues related to drug abuse -- get in line behind those of us who are similarly sick of the same issues related to smoking and alcohol abuse.