Seiling played in the Toronto Maple Leafs junior system from 1960-61 through 1963-64. He won the Memorial Cup in 1960-61 with the St. Michael's Majors and in 1963-64 with the Toronto Marlboros. In 1963-64 he also played with the 1964 Canadian Olympic Hockey Team. He was also be traded to the New York Rangers in the Andy Bathgate trade. He also played for Team Canada in the 1972 Summit Series.