Bigger doesn't necessarily mean better with Canadian marijuana growers. Aphria Inc. (NASDAQOTH:APHQF), for example, claims a market cap that's nearly 4.5 times higher than CannTrust Holdings Inc.'s (NASDAQOTH:CNTTF) market cap. So far in 2018, though, CannTrust has turned in significantly higher stock gains than its larger rival.

But which of these marijuana stocks is the better pick for investors now? Here's what you need to know about how Aphria and CannTrust stack up against each other in the key areas that should make a difference going forward.

Marijuana buds and CBD oil.

Image source: Getty Images.

The case for Aphria

One of the biggest positives for Aphria is its capacity. The company currently can grow 35,000 kilograms of cannabis per year. However, Aphria is boosting its annual production capacity to 255,000 kilograms next year thanks to major expansion efforts that the company stated in its fiscal year 2018 Q4 update were on schedule and on budget.

The largest immediate opportunity for Aphria to use this significant production capacity is in the Canadian recreational marijuana market scheduled to open next month. Aphria has lined up supply agreements for this market with eight provinces and territories so far, including the biggest prize -- Ontario.

Distribution of its recreational cannabis products won't be a problem for Aphria. The company announced in May that it selected Great North Distributors as its exclusive distributor throughout Canada. Great North Distributors is a subsidiary of Southern Glazer's, the largest wine and spirits distributor in North America.

International medical marijuana markets present the biggest opportunity of all for Aphria. Although Aphria CFO Carl Merton said that Q4 international sales were "very minor," the company appears to be in pretty good position to compete globally.

Aphria has operations in Germany, the most important international marijuana market outside of North America. It also expects to become a key player in the United Kingdom, which Arcview Market Research and BDS Analytics predict will be the No. 2 international marijuana market outside of the U.S. and Canada by 2022.

The case for CannTrust Holdings

CannTrust Holdings is eyeing the same growth opportunities that Aphria is. Like Aphria, CannTrust is significantly expanding its production capacity. The company expects to be able to grow more than 100,000 kilograms of cannabis per year by 2019.

CannTrust has secured recreational marijuana supply agreements with four provinces so far: Alberta, British Columbia, Manitoba, and Ontario. The company developed three brands for the recreational market that will be available in Canada beginning in October.

In addition, CannTrust recently formed an exclusive partnership with Breakthru Beverage Group to represent the company's recreational cannabis products. Breakthru is the largest Canadian beverage alcohol broker of premium spirits, wine, and beer brands. It plans to create a separate cannabis-focused sales brokerage company to market CannTrust's products throughout Canada.

The two partners are also looking forward to another recreational cannabis market that won't open for business this year. Canada's regulatory processes for cannabis edibles are expected to be finalized sometime in 2019. CannTrust CEO Brad Rogers thinks that his company's nano-technology for cannabis-infused beverages could give it a competitive advantage in the future.

As for the international opportunity, CannTrust has teamed up with Stenocare on a joint venture to market medical cannabis in Denmark. The company already supplies medical marijuana to Australia. CannTrust has also partnered with Apotex, Canada's largest generic-drug maker, to develop new products for the global medical cannabis market.

Better marijuana stock

Both Aphria and CannTrust can claim something that most of their peers can't: solid profitability. In fact, Aphria is the No. 2 most profitable marijuana stock on the market right now, with CannTrust coming in at third place overall.

Which is the better choice for investors? I think the nod goes to Aphria because of its greater production capacity and more developed international operations.

There's also a wild card for Aphria that could be a game changer for the company. Diageo, maker of Guinness beer, Crown Royal whiskey, and a long lineup of other alcoholic beverage brands, is reportedly looking for a cannabis partner. I suspect that Aphria might be at or near the top of Diageo's list

While Aphria is the better marijuana stock over CannTrust, in my view, keep in mind that both stocks remain quite risky. The share prices of Aphria and CannTrust reflect expectations of tremendous growth. If that growth doesn't turn out to be as great as investors hope -- which is a real possibility -- these marijuana stocks could sink quickly.

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