Canadian marijuana stocks are overvalued, because they are still just commodities, Sean Stiefel, founder and cannabis portfolio manager of Navy Capital, told CNBC on Wednesday.

"We think things have gotten a little bit silly," Stiefel said on CNBC's "Closing Bell." "Valuations now have truly gotten ahead of themselves, and the retail investor here is now buying air, effectively."

Stiefel's comments come amid volatility in medical marijuana company Tilray's stock. The company on Tuesday announced that the Drug Enforcement Agency approved its efforts to export a cannabinoid study drug into the United States from Canada for a clinical trial.

In a wild day of trading on Wednesday, Tilray gave up a 90 percent one-day surge and turned negative, before ending the day up 38 percent, its best day since going public in July. The stock was halted five times on Wednesday by the Nasdaq for volatility.

Recent gains in marijuana stocks have also been fueled by investment from alcohol and beverage companies, and speculation of merger and acquisition activity to come. But Stiefel says Canadian marijuana companies are "essentially just commodity producers," meaning they lack the intellectual property from branding that is so valuable to consumer products companies.

On Oct. 17, when the recreational marijuana market opens in Canada, "all that's going to be out there is flower and low-concentrate oil. There's no branding," Stiefel said.

"The idea somebody is going to spend $5 billion, $10 billion, $20 billion is silly. There is much better assets, much better [intellectual property] outside of Canada — in the U.S., in Israel. You are spending a lot for air," he added.

Stiefel says Canadian companies may dominate in marijuana supply, but in branding, the U.S. will eventually lead.

"The brands that emanate from California are going to be the brands that really do dominate," Stiefel said. "We think brands are going to emanate from the U.S., we think distribution could theoretically emanate from Canada, but at these prices, you're really not getting much bang for your buck up there."

According to Stiefel, "it's very hard to say" whether the sector as a whole is overvalued, but Canada certainly is.

"All you need is the licensing, the manufacturing and the raw ingredients. There's not a tremendous amount of [research and development], with the exception of maybe Canopy and CannTrust, up in Canada that really differentiates anyone up there, versus the plethora of $100 million or less companies sitting in California," Stiefel said.

Earlier on Wednesday, Wall Street trader Jon Najarian warned valuations in the marijuana sector, including Tilray's, are getting out of control.

"This is just stupid time. I can't believe the valuations at this stage," the Investitute co-founder said in an interview on Wednesday.

The trader said he rode some of Tilray's move higher after its IPO, but isn't currently long the shares.

Carter Worth, the Cornerstone Macro technical analyst who last week called a surge in pot stocks, says he thinks Tilray has topped out for the foreseeable future — and may even reverse.

"The high of today, does that stand for a long time? It's my hunch that it does," Worth said Wednesday on CNBC's "Fast Money."

"Pot stocks in general, it's a long run. We have talked about that, this is just the beginning. But this particular stock on this particular day has all the indications of a key reversal, a bad close. The high should be in for a long time," Worth said.

Tilray hit an intraday high of $300 per share on Wednesday before paring some of those gains to close up 38 percent at $214.06. Tilray has skyrocketed more than 800 percent since it began trading on the Nasdaq at $23.05 per share in July.

— CNBC's Tae Kim contributed to this reporting.