More appropriate name would be "dystopia" because banning cash will have mostly adverse effects, intruducing nearly-totalitarian control over the citizens being the most important one.
How would the the DHS or another US entity know about payment transactions made on a canadian bank account?
And, I realize that cannabis is not legal at the federal level in the US, but how would lawfully purchasing a cannabis product years ago disqualify you from entering the US?
But isn't there something like that already for Canadians?
Alas, such a solution would probably be extremely hard to create and therefore never will be.