For a long time, Aphria(NASDAQ:APHA) was overshadowed by its rivals Canopy Growth and Aurora Cannabis. That's changed. Aphria is now arguably at the center of attention in the Canadian cannabis industry, thanks to its pending merger with Tilray(NASDAQ:TLRY). Aphria's shares are up over 180% so far this year. 

But neither the attention nor the tremendous gains are good reasons to buy the marijuana stock. Here's the most compelling reason to buy Aphria right now.

Arbitrage usually involves taking advantage of a price difference of a given stock (or other investment) between multiple markets. But every now and then, an opportunity for a different kind of arbitrage arises. That's what's happened with the merger of Aphria and Tilray.

First of all, this merger isn't one of equals. Aphria is, without question, the dominant company in the deal. Its shareholders will control around 62% of the combined company, and its chairman and CEO Irwin Simon will retain his current roles in the new entity. Aphria will also hold seven of the nine spots on the board of directors.