The obvious solution would be for federal legalization to take place in the United States. That would presumably resolve the problem and may not be that far away. Many states have legalized or are about to. The Democratic Party has the path to legalization as part of its policy platform now. Obviously the current administration isn't terribly interested in that, but that issue may resolve itself in time. It can't be that far away before federal legalization takes place in the U.S. Until then, you are behoven to whatever the U.S. determines.
Of course, it's worth remembering that you have borders with some legalization states as well, so I don't know quite how that's going to work. Presumably, it would be quite strange to stop people who had cannabis convictions from going into states where cannabis is legal. There is this quite strange tension between federal and state law as well.
It's a rapidly evolving field, so this may all change very soon.