TIVERTON, Ontario — Behind a forbidding high-security fence topped with razor wire, Supreme Pharmaceuticals is busy preparing for the legal marijuana trade, with workers expanding a greenhouse complex where the lucrative crop grows.
But while Supreme looks like it will be ready for the day when prohibition ends, Canada’s governments still have a lot of work to do.
Proposing legislation to legalize the recreational use of marijuana was the easy part for Prime Minister Justin Trudeau. With about eight months to go before Canada becomes the second nation after Uruguay to take this step, the federal government and the provinces are staring at a formidable to-do list.
Ottawa still has to set the limit at which drivers will be declared impaired under criminal law, and must determine the rules for advertising and the standards for growers.
Working out most of the details affecting consumers is largely up to the 10 provinces. But only three — Alberta, Ontario and New Brunswick — have offered any idea of how they will operate and regulate their marijuana markets, and then only in the most general terms. The other seven are still in the midst of public consultations.
Two of the most important questions for consumers — how much the legal product will cost and how much it will it be taxed — are still being debated by the two levels of government.
In most of the country, it is still unclear whether marijuana will be sold only in government-run stores. And most provinces have yet to decide the amount of marijuana that individuals will be able to possess or grow.
Nor have most provincial governments decided on the minimum age for buyers, or where smoking marijuana will be legal. The federal government must also explain how it will deal with international drug treaties that prohibit marijuana sales.
Even the precise starting date for legal pot is a mystery.
On top of that, and perhaps counterintuitively, police forces are warning that successful inauguration of a legal system for selling marijuana will require an accompanying crackdown on the black market.
Despite all these challenges, suppliers are optimistic that legal recreational sales will be a reality by summer.
“I 100 percent think Canada will be ready,” said John Fowler, the chief executive of Supreme, which has been selling medical marijuana since 2016. “But I think the real question is: What does ‘ready’ mean?”
The answer, Mr. Fowler said, will be managing expectations in the early days.
“Canadians should not expect that on Day 1, the legal market is going to supply the billions of dollars of illegal cannabis being consumed in Canada,” he said in his windowless office at the greenhouse complex near the shore of Lake Huron where employees work in disposable suits and hairnets to avoid contaminating the multimillion-dollar crop. “That will take time, and I think that’s fine.”
Even with the uncertainty, many investors are betting there is money to be made on legal marijuana. Last month, Constellation Brands, a major wine and beer distributor in the United States, invested $245 million in Canopy Growth, the owner of several licensed medical marijuana growers in Canada.
While the commercial side is upbeat, many provincial leaders say Mr. Trudeau’s timetable of legalization by July — one of his main campaign promises — is unrealistic. Some have demanded a delay.
In a statement, Brad Wall, the premier of Saskatchewan, said that he and several of his counterparts believed a postponement was needed to deal with all the questions.
“Despite these concerns, the federal government has not changed its timetable,” Mr. Wall said.
Speaking with reporters last month, Brian Pallister, the premier of Manitoba, said that his province is reluctantly working to meet the federal government’s schedule.
“That doesn’t mean I like it,” he said. “I’m going to continue to express my concerns about the rapidity of this change.”
But Bill Blair, the former police chief of Toronto and a Liberal member of Parliament tasked by Mr. Trudeau with overseeing the marijuana issue, said that the government will stick with its plan. He dismissed suggestions that the process was rushed, noting that the federal government had been discussing the issue with provinces for two years.
“I don’t minimize the complexity of the work ahead,” Mr. Blair said on Friday. “But by establishing a date for implementation, it’s focused the process.” Further delay, he added, “just facilitates vast windfalls of profit to criminal enterprises.”
Of the three provinces that have released broad outlines, the plans put forth by Ontario and Alberta, although sketchy, treat marijuana much like alcohol.
In Alberta, marijuana will be available in licensed, privately owned shops. Ontario, which has a population of 13.6 million spanning two time zones, will set up 150 government-owned stores. The buying ages will be 18 in Alberta, 19 in Ontario. (Ontario introduced legislation for its new system this past week, but many important details will come later.)
How the provinces and the federal government will divide the tax revenue is still unclear. Governments do not want a repeat of their experience with cigarettes, in which high taxes intended to discourage smoking created a large black market.
Many police forces are among the groups calling for a delay. While a new law will allow the police to use saliva tests to identify marijuana-impaired drivers, what will qualify as impairment has yet to be defined. Little equipment to conduct the tests is now in the field, and few officers have been trained in its use.
“Are we going to be ready?” asked Mario Harel, the president of the Canadian Association of Chiefs of Police and the head of the force in Gatineau, Quebec. “We don’t think so. We’re dealing with a lot of situations so we’re going to be doing our best to be as ready as possible.”
While some Canadians are questioning the accuracy of saliva tests, Robert Mann, a scientist at the Center for Addiction and Mental Health who studies cannabis use, said the tests have proved valid in other countries, although he acknowledged that marijuana’s active ingredient was not as easily measured as alcohol.
His larger concern, he said, is changing public opinion about whether it is safe to drive under the influence of marijuana.
“There’s quite a common perception that you can drive safely under the influence of cannabis,” Dr. Mann said, adding that this view is based in part on now-refuted research from about 20 years ago. “It took quite a while for people’s attitudes about drinking and driving to change.”
The authorities have also faced black-market sales in stores after Mr. Trudeau’s legalization announcement. Cities and provinces have taken different approaches to the black-market shops. In Vancouver, where they are most numerous, officials try to keep control through business licenses. In other areas, particularly Quebec, the police have moved swiftly to close them down.
Mr. Trudeau’s government has repeatedly said that the stores are illegal and will not be a part of the new recreational market.
Brendan Kennedy, the president of Tilray, a licensed medical marijuana producer, said the experience of American states with legalization suggested that the stores will quickly wither away in the face of a legal alternative — provided that “there is adequate supply and adequate locations of legal products.”
Mr. Harel, the police chief, is less certain the black market will vanish anytime soon after legalization.
He anticipates that the illegal market will aggressively promote food laced with marijuana, one of many products that will not immediately be allowed under the new system. In his view, the success of the legal system will rest on swiftly and aggressively shutting down the black market.
“We figure it’s an $8 billion-a-year economy,” he said of illegal marijuana sales. Legalization, he added, will change the dynamics of the black market. “But we don’t think it will fade away.”
By Ian Austen