Foster was taken by the Giants in the first round of the 2011 Bantam Draft at 20th overall. In one year of Midget hockey, the native of Slave Lake, Alberta scored 13 goals and 11 assists in 31 games with the St. Albert Raiders of the Alberta Midget Hockey League in 2011/12. Foster was a member of the gold medal winning Team Alberta at the 2011 Western Canada Under-16 Challenge Cup. The following year, he played on Team Pacific at the World Under-17 Challenge, winning a silver medal. He made his WHL debut on January 28, 2012 against the Edmonton Oil Kings. He scored his first WHL goal on October 20, 2012 against the Calgary Hitmen.