"This does seem to be quite a ludicrous situation, because, as you say, not only is the state of Washington, but three or four other jurisdictions in the United States have legalized marijuana," Public Safety Minister Ralph Goodale told CBC News.

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The latest federal survey data indicate that a little less than half of American adults have used marijuana at some point in their lifetimes. Marijuana use remains illegal for all purposes under federal law.

Any foreign national who admits to having violated his home country's controlled substances laws at any point in the past can be considered ineligible for admission into the U.S.

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"In other words, making an admission to a USCBP [U.S. Customs and Border Protection] officer that you previously violated controlled substance laws in Canada can result in a permanent bar," wrote immigration lawyer Henry Chang for the Huffington Post.

Canadian Prime Minister Justin Trudeau and the Liberal Party have pledged to push for legalization of the recreational use of marijuana in 2017. Ralph Goodale, the public safety minister, told CBC that the current practice of strict prohibition in Canada and the U.S. isn't working.

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"In Canada we're moving in an orderly way to a new regime that will include tight restrictions and regulation, and taxation, and at the end of the day will be more effective in keeping marijuana out of the hands of our kids," he said last week.

Matthew Harvey isn't the only Canadian to be denied entry on account of past marijuana use. The CBC spoke with an immigration lawyer who said he's represented dozens of Canadians in similar situations.

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People entering the U.S. from Canada aren't asked about prior marijuana use as a matter of course. But certain circumstances, often at the discretion of individual border agents, can trigger such questioning. In the case of Matthew Harvey, his career in British Columbia's legal medical marijuana industry may have caused him to be flagged for increased scrutiny.

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In another case, an individual was detained for questioning after border patrol agents found a pouch inscribed with the words "weed money" in his car. The pouch contained neither weed nor money.

People who are barred from the U.S. on account of past drug use can still enter the U.S. if they successfully apply for an "advanced permission" permit. The permit costs $585 and must be renewed periodically.

Other types of criminal behavior present no barrier to entry. A DUI conviction, for instance, does not on its own prevent a person from entering the U.S., according to Customs and Border Protection.

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If Canada legalizes marijuana in 2017 it would likely present additional complications. The current law prevents entry for people who admit to having used drugs "illegally," but by the letter it does not ban people from crossing the border if they use drugs legally. This could create a situation where an agent denies entry to a person not because they currently use marijuana legally, but because they used it illegally at some point in the past.

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"There are certain ironies about the current American position that we will certainly be very vociferous in putting before them," said Public Safety Minister Goodale, "and trying to ensure that Canadians are treated properly and fairly with a lot of common sense, instead of the rather ridiculous situation that's emerged in the last number of days."

Correction: An earlier version of this story misstated how many American adults have used marijuana. That number is less than half.