To say that 2019 was not a banner year for the cannabis industry and marijuana stocks may be understating just how poor things actually went. Despite Canada becoming the first industrialized country to legalize and commence the sale of recreational pot, and momentum for legalization remaining strong in the U.S., the black market has been virtually unstoppable throughout much of North America.

On the bright side, if there is a gleam of light to be found in these struggles, organic growth and ongoing legalizations in the U.S. should lead to significant growth in total cannabis sales in 2020.

America's top-selling marijuana states in 2020

In June, the team of Arcview Market Research and BDS Analytics put out its latest annual report, "State of the Legal Cannabis Markets," which made a number of assumptions and estimates on future growth in Canada, the U.S., and abroad. Though certain aspects of their assumptions have changed (which is to be expected of the nascent, but rapidly evolving, pot industry), the report from Arcview and BDS points to 10 U.S. states surpassing $500 million in full-year marijuana sales in 2020.

Listed in descending order, the top-selling cannabis states in 2020 are expected to be:

1. California: $3.8 billion (recreational and medical mix)
2. Colorado: $1.7 billion ($1.4 billion recreational, $0.3 billion medical)
3. Michigan: $1.21 billion ($299 million recreational, $909 million medical)
4. Florida: $1.2 billion (all medical)
5. Washington: $1.1 billion (recreational and medical mix)
6. Nevada: $960 million ($900 million recreational, $60 million medical)
7. Oregon: $831 million ($796 million recreational, $35 million medical)
8. Arizona: $804 million (all medical)
9. Massachusetts: $682 million ($451 million recreational, $231 million medical)
10. Illinois: $543 million ($270 million recreational, $273 million medical)

First off, you'll note that the report expects California's pot industry to register its first signs of true growth since 2017 this year. Despite its stagnant growth over the past two years, California remains the largest cannabis market in the U.S. by a substantial amount.

You'll also note just how robust sales in Arizona are expected to be, despite the fact that it's solely a medical marijuana-legal state at the moment. Even though Arizonans aren't guaranteed to be voting on a recreational pot initiative come November, it certainly seems likely at this point.

No surprise: MSOs are focusing their attention on many of these key states

What shouldn't come as a surprise is that vertically integrated multistate operators (MSOs) are ensuring that they have a presence in a majority of these top-selling cannabis states.

Perhaps the hottest state at the moment is Illinois, which just commenced adult-use weed sales on Jan. 1, 2020. Illinois became the first state ever to pass a bill allowing for the consumption and sale of recreational weed at the legislative level this past June. By 2024, Arcview and BDS foresee annual sales surpassing $1 billion. Both Cresco Labs (OTC:CRLBF) and Green Thumb Industries (OTC:GTBIF) have vested interests in the Land of Lincoln, with each aiming for the maximum of 10 open locations.

Nevada is another stealthy market that could be a big-time winner for MSOs. Even though the Silver State is slated to hit only $960 million in 2020 sales, Arcview and BDS believe it'll be the leading state for per-capita cannabis spending by 2024 (thanks, tourism). Green Thumb Industries has bet big on Nevada by acquiring Integral Associates in 2019. This acquisition gave Green Thumb eight retail licenses in the state, as well as the only marijuana store presence on the Las Vegas Strip.

And, of course, there's California, which is where all major MSOs want a piece of the pie. Cresco Labs recently went a different route via its now-closed acquisition of Origin House. Rather than buying up dispensary and cultivation licenses, the allure or Origin House is that it's one of only a select few companies to hold cannabis distribution licenses in California. Thus, Cresco Labs buying Origin House gives it access to more than 575 dispensaries in the Golden State.

Here's why things could remain challenging for U.S. pot stocks

While rising sales would obviously bode well for MSOs, there are still a number of issues that U.S.-focused cannabis stocks are going to need to contend with.

For one, marijuana remains illegal at the federal level, and that's highly unlikely to change anytime soon. For MSOs, this means being unable to transport marijuana across state lines, even in instances where two fully legalized states border each other. Instead, MSOs are being forced to set up redundant cultivation and processing operations in every state where they also have dispensaries. This nuisance leads to higher expenses for most U.S. pot stocks.

To build on this point, financing remains a key concern for most U.S. marijuana stocks. With minimal access to basic banking services, many have had to turn to common stock offerings or sale-leaseback agreements in order to ensure that they have enough capital on hand to fund their operations and ongoing expansion. Though Cresco Labs is one of the few MSOs to have (within the past few days) secured traditional forms of financing, access to cash could remain challenging.

Lastly, MSOs are contending with exorbitant tax rates on marijuana in select states. In California, pot consumers can expect state and local sales tax, an excise tax, a wholesale tax, and various fees such as laboratory testing to be factored into the final price of a pot product. High tax rates make it impossible for legal-channel weed to compete with the black market.

Thus, while sales of legal marijuana may be on the rise in 2020, life isn't going to get much easier for publicly traded pot stocks.