Most investors in marijuana stocks will probably say "good riddance" to 2019. Multiple issues plagued the Canadian cannabis industry, in particular, causing many pot stocks to sink this year. But a new year is only days away, with new opportunities on the horizon. 

My view is that 2020 will be a much better year overall for marijuana stocks than 2019 was. And, as was the case last year, some stocks will rise above the rest of the pack. Here are my picks for the three best marijuana stocks to buy in 2020 (in alphabetical order).

1. Constellation Brands

Constellation Brands (NYSE: STZ) was weighed down in 2019 by its 37% stake in Canadian cannabis producer Canopy Growth (NYSE: CGC). But Constellation still delivered a respectable gain of 18%, buoyed by the strength of its premium beer brands Corona and Modelo.

I think that the new year should be a happy one for Constellation shareholders. The company's premium beers are likely to continue dominating the market. My take is that Constellation's anticipated launch in spring 2020 of a Corona-branded hard seltzer should add nicely to sales. I also expect the company's focus on premiumization and brand building with its wine and spirits products should pay off.

Better days should also be on the way for Canopy Growth -- which would be good news for Constellation. The lack of retail stores in Canada has been a huge problem for Canopy, but the situation will improve considerably in 2020 as Ontario issues licenses for new stores. Canopy Growth is poised for success in Canada's nascent cannabis derivatives market in 2020 as well.

Last, but not least, a new CEO takes the helm at Canopy Growth in mid-January. David Klein is stepping down as CFO of Constellation to lead Canopy Growth. Klein is the ideal person to bring much-needed fiscal discipline to the cannabis producer and align Canopy with Constellation's interests. 

2. Innovative Industrial Properties

Innovative Industrial Properties (NYSE: IIPR) shareholders shouldn't have many complaints about 2019. The cannabis-focused real estate investment trust (REIT) stock has soared more than 65% with only two days left in the year.

My view is that IIP should be able to repeat its formula for success in 2020 quite easily. The company currently owns 46 properties in 14 states that it leases to customers. It has plenty of financial flexibility to add more cannabis properties in the new year that will drive even further growth.

Cannabis markets are still in their infancy in several of the states where IIP operates. And with 33 states with legal medical cannabis markets and several likely to vote on legalization in 2020, the company has lots of growth opportunities.

While IIP is poised to deliver strong revenue and earnings growth next year, there's also another reason to like this stock: Its dividend. The company recently declared its fourth-quarter dividend and is paying out 28% more than it did in the previous quarter. IIP's dividend yield now stands at a mouth-watering 5.3%.

3. Valens 

Valens (OTC:VLNCF) definitely wasn't among the group of Canadian marijuana stocks that languished in 2019. The cannabis extraction services provider's shares have skyrocketed 127% year to date. And Valens appears to be poised for an even bigger year in 2020.

I think that Valens just might be the biggest winner of all in Canada's Cannabis 2.0 market. Valens claims multi-year extraction agreements with several of the biggest Canadian cannabis producers, including Canopy Growth, HEXO, Organigram, and Tilray. If these companies' cannabis derivatives products sell well (and I suspect they will), Valens will succeed, too.

Valens should also generate strong growth from its white-labeling deals. Under these contracts, Valens buys cannabis, extracts derivatives such as CBD and THC, packages the final products (edibles, vapes, etc.), then sells the products to a third party who markets them under its own brands. Valens already has white-labeling agreements with BRNT, Shoppers Drug Mart, Iconic Brewing, and Sorse Technology. The company says that it's in negotiations related to over 50 other opportunities.

The Canadian market should be enough on its own to fuel Valens' growth. However, the company could also benefit from international growth. Valens is focusing especially the European, Latin American, and Australian medical cannabis markets. It's also eyeing the U.S. hemp CBD market over the longer term.