Well, Line 5 feeds Line 9, which moves oil from Sarnia to Montreal. If Line 5 were to be shut down, then refineries in Montreal, the Suncor and Valero refineries, would have to source supply either by rail or by truck from western Canada, import it from the United States by the Portland, Maine pipeline or bring it in by tanker down the St. Lawrence and bring in OPEC oil and other supply.
The point I'm making is security of supply. It's an interrelated North American energy market and, if you don't supply it from Alberta, you're going to supply it from somewhere else.