What happened

Shares of Canopy Growth Corporation (NASDAQ:CGC), Cronos Group (NASDAQ:CRON), and Tilray (NASDAQ:TLRY) were up 11.1%, 12.8%, and 18.9%, respectively, as of 3:46 p.m. EDT on Monday. All three are Canadian marijuana growers. And none of them made any announcements that appeared to be catalysts behind the big gains.

So what gives? Probably the best explanation is that large institutional investors could be pouring money into leading marijuana growers, following the news last week that major alcoholic beverage maker Constellation Brands (NYSE:STZ) made an additional $4 billion investment in Canopy.

Marijuana plants on top of increasingly higher stacks of coins

Image source: Getty Images.

So what

After Constellation's huge investment in Canopy was announced last week, I wrote that the deal "radically changes how [investors] should look at the cannabis industry and marijuana stocks, in general." I suspect the action that we have seen today indicates that some institutional investors share that view.

Perhaps the most notable thing, other than the huge gains themselves, is the spike in the number of shares traded today. Canopy Growth's trading volume was nearly five times higher than average, Cronos Group's volume was roughly four times higher than average, and around 58% more shares of Tilray exchanged hands than its average volume. Such surges in trading volume often -- although admittedly not always -- stem from institutional investors scooping up shares.

Constellation's added investment in Canopy (following a $191 million deal last year) likely provided some motivation for institutional investors who had been eyeing initiating or expanding their positions in marijuana growers. The deal further legitimized the cannabis industry. It also hinted at the possibility, and even likelihood, of more deals to come.

Some of Constellation Brands' peers in the alcoholic beverage market could now be feeling the pressure to keep up, rather than fall behind in the development of cannabis-infused drinks. Cronos Group and Tilray would likely be among the top candidates for these companies to approach for partnerships. As for Canopy, the company's management stated that it plans plenty more acquisitions, although there are no plans to acquire any marijuana growers in Canada.

Now what

Investors will no doubt watch anxiously for signs of more dealmaking. In the meantime, Canopy Growth, Cronos Group, and Tilray are busy preparing for the scheduled opening of the Canadian recreational marijuana market in October.

Just because institutional investors are presumed to be investing in these stocks doesn't necessarily mean that other investors should follow. However, it's always a good idea to delve into why big investors might view these stocks in a positive light.

Keep in mind that tremendous growth is already baked into the share prices of all three stocks. There's no guarantee that marijuana markets will expand as quickly as they'd need to in order to justify the stocks' valuations.

In my opinion, Canopy Growth is in the driver's seat in the cannabis industry, thanks to its relationship with Constellation; aggressive investors might want to consider buying the stock. As for Cronos Group and Tilray, a lot rides on what happens with Constellation's peers. However, either of these stocks could still move higher with the expansion of global cannabis markets.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.