Dumping biologic raw sewage in the St Lawrence is a lot different than the potential for polluting with dilbit/oil the freshwater watersheds of Manitoba, Ontario, Quebec that supply drinking water for 80 million people. There is a reason why the existing "East" line is only natural gas and why the oil/dilbit (Enbridge) line travels south of Chicago {largely avoiding the Great Lakes watershed) to get to Sarnia Ontario. 

Built in the early 60s for the National Oil Policy to subsidize Albeta oil,  a surprising consideration for waterways existed then, which appears mostly absent (Ontario) in today's dumbed down world. One would think that the Kalamazoo and Saskatchewan river spills would be considered warnings.