The CEO of California-based marijuana producer and seller Terra Tech is watching the cannabis industry boom north of the border with more than a little apprehension — because he is already seeing the beginnings of an invasion of U.S. markets by Canada's cannabis firms, today the world's largest. "The concern for some of the players is the market will be dominated by Canadian companies, shareholders and banks if we allow too much time to pass," Peterson said by phone from California. With Canada set to legalize recreational marijuana on Oct. 17, Canadian cannabis stock prices have soared, giving these startup firms enormous amounts of money with which to invest in their business.