WESTCOAST ENERGY INC., Vancouver, B.C., agreed to buy the utilities and propane business of Inter-City Gas Corp. (ICG), Winnipeg, Man., for $720 million. Under a related agreement, Westcoast will sell the propane operation to Petro-Canada for $221 million. Westcoast and Petro-Canada will assume $112 million in ICG debt. In addition, new Westcoast subsidiaries will assume liabilities of the new businesses, totaling $485 million at the end of September 1989. Sale is to be complete this spring.