2010-11: Cole Cassels played for the Ohio Blue Jackets U16 team midget team. He scored 11 goals with 23 assists in 37 games and had 61 penalty minutes. He was selected by Oshawa in the first round (16th overall) of the 2011 OHL Priority Draft and drafted in the third round (45th overall) by Muskegon in the 2011 USHL Futures Draft.
2011-12: Cassels skated in 64 games for Oshawa in his first OHL season and played for Canada Ontario in the 2012 U17 World Hockey Challenge. He scored 3 goals with 8 assists and was +1 with 31 penalty minutes with the Generals. Oshawa was third in the East Division. In the six-game playoff series against Niagara he scored 1 goal and was an even plus/minus with 6 penalty minutes. Cassels scored 1 goal with 2 assists and had 6 penalty minutes in six games at the WHC.
2012-13: Cassels returned to Oshawa for his second season and skated in the inaugural CCM All-American Prospects Game. He scored 15 goals with 28 assists and in 64 games for the Generals and was +7 with 61 penalty minutes. Oshawa was second in the East Division and reached the second round in the playoffs. In nine playoff games Cassels scored 1 goal and was -2 with 14 penalty minutes. He was ranked 120th amongst North American skaters in the Central Scouting final rankings and was selected by Vancouver in the third round (85th overall) of the 2013 NHL Draft.
2013-14: Cassels attended his first training camp with the Canucks before returning to Oshawa for his third OHL season. He scored 24 goals with 49 assists, both career highs, and was +7 with 90 penalty minutes in 61 regular season games. He scored 11 power play goals for the Generals. Oshawa finished first in the East Division and reached the Eastern Conference finals. Cassels scored 6 goals with 11 assists and was an even plus/minus with 16 penalty minutes in 12 playoff games. He signed a three-year entry-level contract with Vancouver in December 2013.
2014-15: Cassels had a very strong fourth season with the Oshawa Generals scoring 30 goals and adding 51 assists in only 54 games. He maintained that pace in the playoffs and was a key member of the Generals that took down Connor McDavid and his Erie Otters on the way to winning the Memorial Cup title against the heavily stacked Kelowna Rockets. Cassels displayed leadership and strong two-way play all season on a very good hockey team.
Cassels is the son of former NHL forward Andrew Cassels. While he may not be the flashiest player in the Canucks prospect system, he is likely the most versatile. With a strong two way, defense-oriented game not usually associated with junior hockey players, he can score goals, is above average in the faceoff circle, responsible on the penalty kill, and is willing to block shots. Though somewhat slight of frame he hits regularly. He has a pass-first mentality (much like his father) and that is demonstrated in his assist statistics.