The big day is nearly here. In 36 days, the green flag will officially wave in Canada, opening licensed dispensaries' doors to legal recreational marijuana sales. When the industry is fully operational, it could add up to $5 billion a year in sales, atop what it's already generating from domestic medical weed sales and via exports.

But moving forward, it's probably going to be a lot harder for marijuana stock investors to make money. That's because the time for promises has ended now that Wall Street will be looking for tangible results. This means pot stocks that offer competitive advantages might prove attractive to investors. Throughout the industry, there are four such niche pot stocks that bring massive market share potential to the table.

CannaRoyalty

Possibly one of the more intriguing names for investors to consider is CannaRoyalty (OTC:ORHO.F), which is based in Canada but is very much rooted in California's burgeoning pot market. Though CannaRoyalty got its start as an investment company, nowadays it's looking to corner as much of the cannabis distribution market share as possible in the Golden State.

The interesting thing about California's marijuana industry is that it could be considerably larger than all of Canada's. After all, California does have the fifth-largest economy in the world. Though the state will have thousands of branded pot products on dispensary shelves, as well as hundreds of potential dispensaries, there is just a handful of distributors like CannaRoyalty, giving these middlemen a critical but profitable role.

Recently, CannaRoyalty has been actively gobbling up distribution companies and infrastructure in California faster than folks can blink. Following the buyout of Alta and River, it acquired Kaya and FloraCal. It's unclear exactly how much market share CannaRoyalty will be able to grab via acquisitions, but whatever it does grab should yield predictable cash flow, year in and year out.

Kush Bottles

Another pot stock that could surprisingly cull quite a bit of market share within its respective niche is Kush Bottles (OTC:KSHB). Though Kush is involved in the vaporizer business, its real calling in the cannabis industry could be the role it plays in both marketing and packaging, as well as via cannabis-oil production.

With regard to marketing and packaging, Health Canada put out a set of relatively strict guidelines that marijuana companies would have to adhere to if they wanted their products on dispensary shelves. This will mean working with marketing and packaging companies like Kush Bottles to ensure compliance with Health Canada's marketing, packaging, and branding laws. Kush will also be responsible for helping these pot stocks develop a brand identity.

Additionally, Kush Bottles' acquisition of Summit Innovations moves it into the hydrocarbon gases market. Hydrocarbon gases are one of a handful of essentials when producing cannabis oils. Since oils are expected to be a hot commodity with growers due to their higher margins than dried cannabis, Kush may be setting itself up to be a much-needed middleman in the production process.

GW Pharmaceuticals

Not all marijuana stocks grow the green stuff right out of the ground. U.K.-based GW Pharmaceuticals (NASDAQ:GWPH) is a cannabinoid-based drugmaker that does its damage in the laboratory.

On June 25, GW Pharmaceuticals became the very first drugmaker to get the thumbs-up for a cannabis-derived drug known as Epidiolex from the U.S. Food and Drug Administration (FDA). Sure, synthetic forms of cannabis, such as dronabinol, had been previously approved, but no cannabis-derived drug in history had ever been given a green light by the FDA.

Epidiolex, a cannabidiol-based oral solution -- cannabidiol is the cannabinoid best known for its perceived medical benefits -- wound up running circles around the placebo in multiple pivotal-stage studies for patients with two forms of childhood-onset epilepsy. One of these ailments, Dravet syndrome, had no previously approved medicines, meaning Epidiolex should be able to grab nearly all market share in this indication. Though GW Pharmaceuticals is bound to face competition sooner rather than later, its lead drug is nonetheless expected to push the company into the black on a recurring basis.

Innovative Industrial Properties

Last but not least, there's marijuana-based real estate investment trust (REIT) Innovative Industrial Properties (NYSE:IIPR).

An REIT is a company that acquires real estate assets in a particular industry, then leases those assets out for an extended period of time, earning revenue via rental increases amid a relatively fixed-cost model. As for Industrial Innovative Properties, it now has more than a dozen medical marijuana-growing properties in the U.S., each of which was initially leased out for between 15 and 20 years. Annual rental inflation hikes are passed along with each of these lease deals, as well as a 1.5% management fee. Or in other words, it should easily be able to stay ahead of the inflationary curve.

The beauty of the cannabis-REIT model is that it should also generate predictable profits. With the U.S. federal government sticking to its Schedule I classification of weed, it means that cannabis grown within a state must stay in that state. That essentially gives Innovative Industrial Properties the incentive to purchase medical marijuana grow facilities in a variety of legalized states.

To boot, investors should receive an above-average dividend with this stock. It's certainly one for marijuana stock investors to consider.