Sifers began his hockey career by playing at the University of Vermont. He led all Catamounts defensemen in scoring for three consecutive seasons, finishing the 2005-06 season with 3 goals and 18 points in 38 games. Sifers was also captain of the university team, and was named an honorable mention to the Hockey East All-Conference team. He finishes his four-year career at the University of Vermont with 15 goals and 70 points in 143 games. Sifers was also just the second three-time team captain in the program’s history.
Sifers was signed to an entry level contract by the Maple Leafs during the 2005-06 season, and was assigned to the Toronto Marlies of the American Hockey League. Sifers played 2 games in that year for the Marlies. In his first full season with the Marlies in the 2006-07 season, Sifers scored 7 goals and 25 points in 80 games. Sifers' production dropped in the 2007-08 season, scoring only 3 goals and 13 points in 80 games.
Sifers began the 2008-09 season with the Marlies again, but was recalled by the Maple Leafs on December 6, 2008. Sifers made his NHL debut on December 8, 2008 against the New York Islanders.