That's unusual. If a border official does a Google search and finds that you've got any relationship with marijuana, they're likely to bar you from entering, at least at that time, and for up to 30 days and possibly permanently. There are lots of examples of Canadians now permanently barred. The former mayor of Grand Forks, Brian Taylor, found himself barred from going back there. He used to go over there to buy milk and eggs, amazingly, and I don't know why that's reasonable, but it's so close to Grand Forks that he used to go. Now he's barred from doing so because he's had a relationship with marijuana; he's advocated as mayor.
The border states of Washington, Vermont, Maine, New York, Wisconsin, and Minnesota all have medical marijuana or legalization regimes. The entire border with the exception of Idaho and Montana, and Pennsylvania, which is not so much on a border but across the lake, are the only three states left that don't have some kind of medical or legal regime going on in the United States, so this argument that we're going to have a trade problem is diminished. What we're going to have is a border problem.
One of the things they haven't thought of with the Ontario monopoly is that every employee who works for the Ontario cannabis control board is going to be barred from entering the United States. So as long as part of their employment they're willing to admit they're never going to the United States again, then that's fine. I'm sure they'll get employees. We in the free market already acknowledge this, that we're not going to be able to travel to the United States if we have a relationship with cannabis that's in any way public. I suspect every government employee who wants to work for a marijuana shop might want to consider if they have family in the United States or if they ever go to the United States because they're going to be barred.