OTTAWA - Canada's chief NAFTA negotiator says only limited progress has been made in revamping the continental trade pact. Steve Verheul says that's because the talks are moving "a bit too fast." The seventh round of NAFTA talks is set to begin later this month in Mexico City with substantial differences remaining on autos, a sunset clause and an investor-dispute resolution mechanism, and U.S. demands for greater market access to Canada's protected ...