Shares of Canopy Growth Corporation (NYSE: CGC), Cronos Group (NASDAQ: CRON), and Tilray (NASDAQ: TLRY) were up 11.1%, 12.8%, and 18.9%, respectively, as of 3:46 p.m. EDT on Monday. All three are Canadian marijuana growers. And none of them made any announcements that appeared to be catalysts behind the big gains.So what gives?