Enbridge (ENB +2.71%) is the Canadian midstream company responsible for transporting 70% of the Canadian oil that the United States imports from our northern neighbor.  The midstream giant returned close to 15% this year, but one of its biggest hopes for future growth -- its Northern Gateway pipeline project -- may be stymied because of political and environmental opposition.  In this video, energy analyst Aimee Duffy takes a look at what is contributing to the Canadian company's woes and how an oil industry precedent could point toward a light at the end of the tunnel.