It shouldn't take very long for things to get interesting for marijuana stocks in 2020. There are plenty of potential catalysts that could be on the way, both in Canada and in the U.S.

But I think that investors should especially keep their eyes on three marijuana stocks in January: Aphria (NYSE:APHA), Canopy Growth (NYSE:CGC), and Cresco Labs (OTC:CRLBF). There's plenty to watch with each of these stocks early in the new year.

1. Aphria

The biggie to look forward to with Aphria is the company's fiscal 2020 second-quarter update on Jan. 14. If those results are along the lines of what Aphria delivered in the first quarter, investors could be happy campers.

Aphria's crown jewel is its German medical cannabis distribution subsidiary, CC Pharma. Expect the company's German business to contribute at least half of total revenue in Q1. And since the acquisition wasn't completed until January 2019, CC Pharma will almost certainly fuel strong year-over-year revenue growth for Aphria.

However, Canada's "Cannabis 2.0" market for cannabis derivative products won't be a factor in Aphria's Q2 results. That's because the company's fiscal second quarter ended on Nov. 30, a few weeks before the first cannabis derivative products for this new market began to ship. Aphria could provide some color on how sales are going so far in the Cannabis 2.0 market in its quarterly conference call, though. If so, it could be eye-opening since Aphria is the first major Canadian cannabis producer to provide an update in 2020. 

2. Canopy Growth

Canopy Growth won't announce its quarterly results until mid-February. It's possible, though, that the company could give some hints about how business is going during January. However, there's another important reason to watch Canopy this month: A new CEO will take the helm on Jan. 14.

David Klein joins Canopy Growth after serving as CFO for the company's big partner and largest shareholder, Constellation Brands (NYSE:STZ). He's no stranger to Canopy after serving on the company's board of directors for more than a year and as chair of the board since October 2019.

My hunch is that Klein will grant several interviews this month with the considerable interest level among investors as to which direction he'll take Canopy Growth. A more disciplined financial path for the company seems to be a shoo-in. As CFO of Constellation, Klein was fully aware of the negative impact that Canopy has had on the big alcoholic beverage maker's financial performance.  

3. Cresco Labs

There are at least two key things to watch with Cresco Labs in January. One is how well the launch of Illinois' adult-use recreational marijuana market goes. Cresco announced its first sales to 3,445 customers at five of its dispensaries on New Year's Day. Any reports -- either positive or negative -- about the new market will likely affect Cresco's share price. The company has prioritized the opportunity in its home state.

The other thing to keep your eyes on with Cresco in January is the potential closing of its acquisition of Origin House (OTC:ORHOF). This deal was first announced on April 1, 2019. For a while, investors might have wondered if the acquisition was merely an April Fool's prank after progress on the transaction dragged on for months.

But Origin House shareholders overwhelmingly approved revised terms of the acquisition on Dec. 31. The two companies now await a final court order, which is expected by Jan. 6. The transaction should be finalized shortly after receipt of the court order. Adding Origin House's California distribution operations and growing lineup of cannabis brands will make Cresco an even more formidable player in the U.S. cannabis industry.