It's here.

Today is the day that Canada opens the doors to its nationwide legal recreational marijuana market. As you might expect, many investors are focusing like a laser on what happens in the early days of this new market. And that laser focus is aimed at the biggest Canadian marijuana stocks.

A game of musical chairs has been played over the last few months, as different marijuana growers moved up and down in the ranking of the largest Canadian marijuana stocks by market cap. Which stocks are at the top as Canada's adult-use recreational market opens? Let's size up the five biggest Canadian marijuana stocks, which (in alphabetical order) are Aphria (NASDAQOTH:APHQF), Aurora Cannabis (NYSE:ACB), Canopy Growth (NYSE:CGC), Cronos Group (NASDAQ:CRON), and Tilray (NASDAQ:TLRY)

Five increasingly taller stacks of coins with marijuana plans on top of them

Image source: Getty Images.

5. Cronos Group

Cronos Group enters the big day with a market cap of close to $2 billion, enough to rank fifth among Canadian marijuana stocks. And it's nearly double the market cap that Cronos claimed at the beginning of 2018. 

Right now, Cronos has an annual production capacity of around 6,650 kilograms. But the company is adding a fourth indoor building at its Peace Naturals facility in Ontario that should boost its capacity by 33,500 kilograms per year. Cronos has also partnered with Bert Mucci, owner of Mucci Farms, on a joint venture that will add 70,000 kilograms of annual production. On top of these domestic expansions, Cronos is increasing its growing space in Australia and Israel.

4. Aphria

Aphria takes the No. 4 spot with a market cap of roughly $3.2 billion. Although the company's share price is up by only a single-digit percentage so far in 2018, its market cap has increased by more than 50%. (Issuance of new shares to generate cash explains the difference.)

On day one of Canada's recreational marijuana market, Aphria's annual production capacity totals around 34,500 kilograms. But expansions at its Aphria One and Broken Coast facilities plus its big new Aphria Diamond facility will increase the company's capacity to 255,000 kilograms by early next year.

3. Aurora Cannabis

Coming in third among the big five Canadian marijuana stocks is Aurora Cannabis. The company's market cap is currently close to $10.2 billion. That's more than triple Aurora's market cap at the outset of 2018. This big jump stemmed largely from multiple acquisitions made by Aurora over the last year, notably including the buyout of MedReleaf.

Aurora's current annual production capacity is 45,000 kilograms. But by the end of the year, the company anticipates that its capacity will have jumped to more than 150,000 kilograms. And once several other major expansion projects are completed in the second half of 2019, Aurora's production capacity should soar to more than 500,000 kilograms per year.

2. Canopy Growth

For most of the last couple of years, Canopy Growth sat at the top of the largest Canadian marijuana stocks by market cap. Now, though, Canopy's market cap of around $10.9 billion puts it in second place. It's not that Canopy's market cap hasn't increased. Actually, it's up nearly 150% so far this year. But another stock leaped past Canopy.

Canopy Growth doesn't talk in terms of production capacity. The company does, though, discuss its 4.3 million square feet of growing space licensed for production in Canada. And Canopy claims 5.6 million square feet of growing space in total. That's higher than any other marijuana grower's growing platform -- including Aurora's total projected growing space of 4.5 million square feet.

1. Tilray

Tilray holds the No. 1 spot among Canadian marijuana stocks with a market cap of nearly $15 billion. The stock began trading on the Nasdaq exchange in July and has skyrocketed pretty much ever since. Tilray's market cap topped Canopy's by September and has remained the largest in the industry over the last several weeks except for a brief period.

But Tilray doesn't claim a top ranking in production capacity. The company expects to have 912,000 square feet of growing space by the end of 2018 -- 682,000 square feet of which is in Canada, with the rest in its Portugal facility. 

Changing positions?

The companies in the top 5 could easily change positions over the next few months. Which is the most likely to lose ground? Probably Tilray.

Tilray's rapid rise has been fueled in large part by a very low stock float and a high level of short-selling, which combined to result in a short squeeze that continues to play itself out. However, Tilray's IPO lockup period expires on Jan. 15, 2019. There could be an increase in shares sold at that time, creating pressure that pulls the stock down. 

It seems likely that Canopy Growth will eventually reclaim its spot at the top. However, Aurora Cannabis could make a run. Its stock will soon list on the New York Stock Exchange, making Aurora more visible to U.S. investors. The company could also be a top candidate to partner with a major beverage maker outside of the cannabis industry.

Ultimately, though, what matters most for investors isn't market cap rankings, but growth instead. All five of these Canadian marijuana companies should enjoy strong revenue growth. Of the group, Aphria might be in position for the most growth in its share price thanks to its relatively attractive valuation among marijuana stocks.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends Nasdaq. The Motley Fool has a disclosure policy.