You hear about Canadian marijuana stocks all the time. But what about the stocks that do business day in and day out in the biggest marijuana market in the world? If you're wondering, that's the United States. 

While Canada's legal recreational marijuana market has received a lot of attention, and deservedly so, nearly 80% of all worldwide marijuana sales this year will be made in the good old USA. And there are some intriguing marijuana stocks that operate in the U.S. market.

The three biggest marijuana stocks by market cap that maintain significant U.S. operations, excluding cannabis-focused biotechs, are Scotts Miracle-Gro (NYSE:SMG), MedMen Enterprises (NASDAQOTH:MMNFF), and MariMed (NASDAQOTH:MRMD). But bigger isn't always better. Are these three top U.S. marijuana stocks smart picks for long-term investors to buy?

1. Scotts Miracle-Gro

Scotts Miracle-Gro is the biggest marijuana stock in the U.S., with a market cap of $4.5 billion. The company is best known for its many consumer lawn and garden products, and Scotts' core lawn and garden business still generates over half of the company's total revenue.

But Scotts is also a major player in the marijuana industry. In fact, its Hawthorne Gardening subsidiary is the leading supplier of hydroponics products to U.S. cannabis growers. Hawthorne has made multiple acquisitions over the past few years, with the most significant one completed last year with the purchase of Sunlight Supply. 

There are several dynamics that should work in Scotts' favor in the coming years. More states have legalized medical and/or recreational marijuana, and potentially more are on the way. California is working out some of the issues that caused a rocky start for the launch of its legal recreational marijuana market last year. And Scotts has introduced new organic products that should drive growth for its core lawn and garden business. 

2. MedMen

MedMen takes the No. 2 spot among U.S. marijuana stocks, with a market cap of $1.5 billion. The company is the leading cannabis retailer in the U.S. and continues to expand. 

The most important market for MedMen is in California. The company has captured around 5.3% of the retail cannabis market in the state with its nine existing stores that outperform many high-end retailers outside the cannabis industry in sales per square foot. MedMen plans to build to open at least six more stores in California in the future.  

MedMen's pending acquisition of PharmaCann would be the biggest deal in the history of the U.S. marijuana industry. Once the transaction is complete, MedMen will be licensed for 77 retail stores in 12 states. In addition, MedMen is partnering with Cronos Group to launch retail cannabis stores throughout Canada.   

3. MariMed

MariMed is the third largest U.S. marijuana stock, with a market cap of more than $780 million. It was one of the top performing U.S. marijuana stocks of 2018, racking up a gain of 371%.

The company initially focused exclusively on providing advisory services to marijuana businesses. These services included the design, development, and operation of medical marijuana cultivation facilities and production centers as well as dispensaries. Now, though, MariMed is buying the operations from its customers.

While MariMed continues to expand in the medical marijuana market, it could also have a great opportunity ahead with the U.S. legalization of hemp in December 2018. The company invested in hemp grower GenCanna late last year and now has a subsidiary that focuses on the hemp cannabidiol (CBD) market. 

Are they buys?

It's entirely possible that all three of these top U.S. marijuana stocks perform well in 2019. That would especially be the case if substantial progress is made toward changing federal laws that would recognize the rights of states to enforce their own marijuana laws.

My view, though, is to wait and see on two of these stocks. I'd prefer for MedMen's acquisition of PharmaCann to close and then watch how well the company executes on its strategy to dominate the retail cannabis market in the United States. And while I think MariMed's strategy of acquiring operations from customers and entering the hemp CBD market is smart, I'd still rather hold off to see how things unfold.

I like Scotts Miracle-Gro, though. The stock took a beating last year, with issues in California's rollout of legal recreational pot and an unusually late start to spring, which negatively affected Scotts' sales of lawn and garden products. But things are looking up for the company now. I think Scotts will be a winner over the long run and see it as a good stock to buy at its current price.