Cannabis is already big business in Canada. The drug was approved for medicinal use 20 years ago, and almost 30 percent of young adults say they use it recreationally. The world’s biggest marijuana companies have grown up in Canada. While the recreational pot business in the eight U.S. states where it’s legal still deals almost entirely in cash, Canada is home to several large pot corporations that trade on the Toronto Stock Exchange. The biggest, Canopy Growth Corp., with a market value of C$1.67 billion ($1.24 billion), produces more marijuana than any other entity in the world.