While we know the exact date marijuana will become legal in Canada – Oct. 17 – the American timeline remains hazy.

It’s possible to imagine a Democrat-controlled Congress and White House in the not-too-distant-future repealing pot’s prohibition under the Controlled Substances Act and officially delegating the matter to the states. It’s equally conceivable, however, to imagine a prolonged era of Republican rule preserving the status quo. Perhaps, as evidence of marijuana’s harm accumulates, a bipartisan consensus will emerge to double down on outlawing the drug in some new and creative way.

All we really know is that come this autumn, the United States and Canada are poised to enter a new era of disunity in a major realm of criminal law. At a time when the cause of U.S.-Canada integration is already snared on the rocks of President Trump’s trade war, Prime Minister Justin Trudeau’s pot initiative can only slow things further.

The irony is that many U.S. states already have marijuana regimes far more liberal than Canada’s, having legalized pot for personal use years ago. In doing so, they called their federal government’s bluff that it would not trample upon such a self-confident evocation of federalism, particularly in the context of growing ambiguity about the morality of drug prohibition. (The Obama administration made its distaste for enforcement explicit.) Yet, because borders and immigration remain firmly under Washington’s jurisdiction, mandate that is not nearly as disputed or unpopular, the federal government enjoys a free hand to enforce marijuana prohibitions against foreigners with a strictness it would never extend to its own citizens.

Journalists on both sides of the border like to highlight stories of Canadians who have attempted to enter the United States for innocuous reasons, only to be slapped with extreme punishments for minor pot-related offenses committed ages ago. In 2013, for instance, a man from Vancouver Island was unable to claim an all-expenses-paid trip to Super Bowl XLVII after U.S. customs agents at Toronto’s international airport discovered he had been convicted of possessing two grams of marijuana in 1981. A recent story in The Washington Post described a young British Columbian woman who tried to attend a Dave Matthews concert in Washington state but wound up getting banned from the United States for life after her admission to a border guard that she smoked marijuana in the past. “I mean who hasn’t had a puff of a joint?” she said. There has been speculation that Trudeau himself may not be able to visit the United States once his diplomatic immunity lapses, given his past admissions of pot smoking.

The Trump administration, for its part, has been firm that there will be no lessening of this sort of thing once Canada’s laws change, reciting standard boilerplate about the need to “enforce federal law” to anyone who asks. The administration has built its brand vowing to impose a blunt and unforgiving style of border security, and while harsh tactics at the southern border have captivated the world, time will tell whether there will eventually be a northern manifestation, too.

For the time being, however, Canadian travel and immigration to the United States have not visibly abated. Defying the expectations of many, rates appear to have actually gone up since Trump’s election. As much as a certain sort of Canadian may loudly affect an anti-American persona, many speak louder with their actions, continuing to travel and move to the United States in enormous numbers, regardless of politics.

Trump or no Trump, after all, for any Canadian interested in shopping, sport, culture or recreation, the United States remains an indispensable destination. There’s simply no Canadian equivalent of things such as New York’s Fifth Avenue, the U.S. Open, San Diego Comic-Con or Miami Beach.

For Canadians aspiring to join the next generation of super-capitalists, meanwhile, the United States’ pull is no less strong. Silicon Valley makes ample use of Canadian labor, and not just at the lower levels. The National Foundation for American Policy identified eight American billion-dollar start-ups created by Canadian immigrants, including mainstays such as Slack and Uber. So long as Canada’s economy continues to suffer from its traditional impairments in the realms of innovation, productivity, competitiveness and creativity, the United States will magnetize Canadians who possess such skills in abundance. But increasingly, the skill of self-control will be required as well.

Legalization of a product tends to increase its consumption, especially when that legalization is accompanied by the creation of a robust, competitive retail industry to sell it, as Trudeau’s government promises will be the case with legal marijuana. If Canadian pot usage rises after legalization’s soft encouragement, a new generation of Canadians may soon find that their government’s decision to normalize this “victimless crime” has in fact victimized their American dreams.

The notion that consuming marijuana presents any real health danger has been widely mocked by legalization’s advocates, including Canada’s multibillion-dollar pot industry, who have an obvious interest in portraying their product as harmless. The goal of discouraging pot’s use — which Ottawa, despite legalization, still nominally favors — thus faces an uphill battle in the context of a culture primed to be skeptical of anything reeking of “Reefer Madness.”

A modest suggestion for Canada’s marijuana critics: They should propose that all packaging of legal pot bear a label with an indisputable claim, “WARNING: Use may result in loss of access to America.” That might actually get Canadians to think twice before toking.