Mark Hill, a co-founder of Canada's no-frills carrier WestJet Airlines, resigned late Wednesday amid an increasingly acrimonious legal fight between Air Canada and WestJet over suspected industrial espionage. Mr. Hill's abrupt resignation is the latest in what promises to be a drawn-out court fight between Air Canada, the country's leading airline, and WestJet, a low-cost upstart based in Calgary. In a brief statement Wednesday night, WestJet said the departure was related to ''the ongoing scrutiny of Mr. Hill's actions.'' Air Canada, which is preparing to emerge from 15 months of bankruptcy protection, filed suit in April against WestJet, contending that Mr. Hill monitored an internal Air Canada Web site.