Hexo Corp. has drawn interest from an occasional activist investor, who fears the Canadian marijuana company will miss out on a frenzy of deal making in the budding industry.

New York-based Riposte Capital LLC, Hexo’s second-largest shareholder with a roughly 2.5% stake, published a letter Thursday urging the company to explore strategic alternatives and take advantage of the cannabis sector’s rapid growth. The options could include selling the company, seeking a merger partner or soliciting a large investment from Molson...