As Calgary-based Enbridge Inc. continues its legal battle with the state of Michigan over Line 5, a former Alberta oil executive says closure of the pipeline would choke one-fifth of Canada’s crude oil exports and upend supply chains for diesel and gasoline production on both sides of the Canada-U.S. border. “They would do all kinds of things, shipping by rail, by truck and even ship to meet market need. But in my opinion there would be shortages for quite a bit of time,” Richard Masson, an executive fellow at the University of Calgary and chair of World Petroleum Council Canada, said in an interview. “And we haven’t been able to build pipelines without delays and controversies for years, so there’s no real way to replace Line 5. What we need is that pipeline to keep running.” While U.S. President Joe Biden’s cancellation of Keystone XL hurt Canada’s oilpatch, now the …