What happened

Marijuana stocks Canopy Growth (CGC -4.68%), Aphria (APHA), and Tilray (TLRY) all jumped in early Tuesday trading, but for different reasons.

In the case of Canopy, it's a new line of CBD products for pets from a famous name that drove the shares 7.8% higher as of 10:45 a.m. EST today. Aphria and Tilray, two companies still in the midst of merging with each other, got a boost from across the ocean. Aphria stock was up 7.2%, and Tilray gained 11.5%.

Rising stock chart is labeled Cannabis Inc with dollar signs and marijuana leaves decorating

Image source: Getty Images.

So what

This morning, Canopy Growth announced it is launching a line of "scientifically backed CBD wellness solutions for canines developed by Martha Stewart with her own beloved dogs in mind."  

Canopy will provide the cannabidiol ingredients for Martha Stewart to produce a line of oil drops and soft-baked chews. The aim is to support pets' mental and physical well-being, reduce the effects of everyday stress, and maintain joint health and mobility. The products appear to be designed for dogs only, with no mention of cats in the press release. The company noted that it has also partnered with Stewart on a line of hemp-derived supplements for humans.

Aphria and Tilray are benefiting from the decision by France's National Agency for the Safety of Medicines and Health Products to pick Tilray to supply certified medical cannabis products for experimentation in France.  

Tilray will supply cannabis from its Portuguese production facility to the French agency over 18 to 24 months beginning in the first quarter of 2021. France intends to test medical marijuana's effectiveness in the treatment of a variety of ailments including neuropathic pain, epilepsy, multiple sclerosis, and cancer.

Now what

As the headlining company name in the announcement from France, Tilray is naturally enjoying the bulk of the stock gains today -- naturally, but not necessarily correctly.

Tilray and Aphria are on track to become one and the same company, so it doesn't make a lot of sense for Aphria's price gains today to be so much lower than those of its soon-to-be partner. If one stock goes up, the other should go up just as much, especially since the merger is being structured as a sale of Aphria to Tilray, with the latter paying for the former with Tilray shares.  

Of the two big announcements in marijuana today, the Tilray news offers investors the best "arbitrage" opportunity by buying shares of Aphria before they go up even more.