Canada's nationwide recreational marijuana market opened last October; last week, we got results from Canada's two biggest marijuana companies that suggest the country's marijuana market represents a massive opportunity.

The possibility of capturing billions of dollars in legal marijuana sales in Canada only hints at the larger opportunity associated with legalization of marijuana globally. If you think increasingly more countries will follow Canada's lead, then it could be smart to buy shares in Canopy Growth (NYSE:CGC), Aurora Cannabis (NYSE:ACB), and Cronos Group (NASDAQ:CRON) in 2019.

The biggest marijuana company

Canopy Growth is Canada's biggest marijuana company. A vertically integrated pot play, Canopy Growth grows marijuana in state-of-the art greenhouses, processes it using the latest in automated machinery, packages it, and sells it throughout Canada.

"2019" painted on a road that stretches into the distance

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The company's investments in growing capacity early on allowed it to capture over 30% of Canada's medical marijuana market. Based on its latest quarterly results, leveraging its size and brand recognition is allowing it to capture at least as much market share in Canada's emerging recreational market.

Last quarter, selling into every Canadian province's adult-use market catapulted Canopy Growth's revenue to 83 million Canadian dollars, up 282% from the same quarter last year. Last quarter only included about six weeks of recreational sales, and demand outstripped supply early on, crimping revenue. So there's good reason to believe sales will head a lot higher.

Canopy Growth is also establishing itself in other countries that are breaking down barriers to marijuana; it has operations in Europe, Australia, and Latin America. It also recently announced plans to enter the United States for the first time.

Until recently, Canopy Growth couldn't operate in the U.S. because of rules prohibiting publicly traded companies from engaging in businesses that are illegal at the federal level. Marijuana remains a Schedule I drug in the U.S. However, the latest Farm Bill removed hemp, a non-psychoactive form of cannabis, from the controlled substance list in December. Following hemp's reclassification, Canopy Growth plans to spend up to $150 million in New York state to create a hemp industrial park.

The U.S. market for hemp-based products is already worth hundreds of millions of dollars per year, but it could become a multibilion-dollar market if new products are made using hemp-derived extracts. Importantly, Canopy Growth's hemp facilities could be converted to process marijuana someday. Therefore, if marijuana becomes legal nationwide, Canopy Growth's hemp strategy could give it a valuable head start in what's estimated to be a $50 billion market opportunity.

A mad rush of production growth

Investors should also consider buying Canada's second-largest cannabis company, Aurora Cannabis. Aurora Cannabis doesn't have Canopy Growth's market share, but it's arguably best-positioned to give it a run for its money.

The company's acquisitions of CannaMed and MedReleaf last year turned it into one of the biggest medical marijuana suppliers in Canada, and a robust expansion plan that includes significant increases in annual marijuana production offers strong revenue tailwinds.

Last quarter, Aurora Cannabis reported that acquisitions and initial adult-use sales in Canada caused its sales to skyrocket 363% to CA$54 million. The adult-use market accounted for CA$21.6 million in sales, giving it (the company estimates) a market share of roughly 20%.

The company sold nearly 7,000 kilograms of marijuana or marijuana equivalents, such as extracts, in the quarter -- up 502%. However, that figure could increase substantially because of new production coming online from expansions to greenhouses, including Aurora Sky. Currently, management says annual marijuana production capacity is running at about 120,000 kilograms, but that's expected to increase to 150,000 kilograms next month. If so, then Aurora Cannabis expects to have 25,000 kilograms of marijuana available for sale by the end of June.

Aurora Cannabis's future plans include boosting annual production above 500,000 kilograms; if it can accomplish that, it could see its gross margin improve considerably. Last quarter, its gross margin was 52%, but that reflected average production costs of $1.92 per gram. Aurora Cannabis believes the new production it's bringing online at Aurora Sky and elsewhere will be at cost below $1 per gram.

Given the company's potential sales growth and improved gross margin as new supply comes online, its future appears bright.

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A powerful partner

There are marijuana companies that are bigger than Cronos Group by revenue and planned marijuana production. But Cronos and Canopy Growth are the only two cannabis companies with significant financial firepower and access to supply-chain, branding, and regulatory expertise because of investments from major consumer-goods companies. Cronos Group sold 45% of itself to tobacco powerhouse Altria (NYSE:MO) for $1.8 billion in December; this followed Canopy Growth's decision to sell 38% of itself to alcohol giant Constellation Brands (NYSE:STZ) for roughly $4 billion last August.

Having Altria as a partner is a big win for Cronos Group. Altria owns the U.S. Philip Morris tobacco brands, including Marlboro cigarettes, and it has extensive experience navigating regulatory scrutiny. It's built up a slate of successful brands, and it has extensive relationships with farmers and other suppliers. Additionally, Altria owns over 30% of Juul, a leading vape company that theoretically could provide Cronos Group with some intriguing collaboration opportunities.

Cronos Group hasn't reported results for the calendar fourth quarter yet, so we don't know how it did after recreational sales began in Canada -- but sales jumped 186% year over year to CA$3.8 million in the third quarter, so its products appear to be gaining traction. Its annualized production capacity was just 6,650 kilograms in Q3, but it has said that capacity will reach 40,150 kilograms this year and that it plans to produce 117,000 kilograms per year. Those predictions were prior to Altria's investment, so you could see Cronos Group announce new targets during its next earnings release.

During Altria's fourth-quarter earnings call, it highlighted a forecast for legal marijuana sales of $40 billion per year, based on current legal markets. It also said worldwide legalization could increase that market opportunity to $250 billion. Given those figures and Altria's help, it could be smart to own Cronos Group for the long haul, too.

Check out the latest Cronos and Canopy Growth earnings call transcripts.