Finucan began his lacrosse career as a coach for the Brantford Minor Lacrosse Association, in 1968. He became a part owner of the Brantford Warriors Lacrosse Team in 1970. This team dominated the sport and won the Canadian Mann Cup in 1971. In 1973, he became Director of Player Personnel and Assistant Manager of the Rochester Griffins, in the Professional National Lacrosse League. His team won the League's first championship in 1974 and he was awarded “Manager of the Year". He was also the manager for the NLL champions, the New York Long Island Tomahawks, for three years before returning to Brantford.