On December 23, 2016, Bruin was traded to the Seattle Sounders in exchange for undisclosed amounts of general and targeted allocation money. Bruin made his Sounders debut on March 4, 2017, coming on as a substitute in a 2–1 loss against his former team, the Houston Dynamo. He scored his first Sounders goal on March 11, an equalizer in the 94th minute of a 2–2 draw against the Montreal Impact. He scored a brace on October 15 to help the Sounders defeat FC Dallas 4–0. Bruin ended his first season in Seattle with 11 goals and 2 assists from 31 regular season appearances, helping the Sounders finish second in the Western Conference. After Bruin started both legs of a 2–0 aggregate win against the Vancouver Whitecaps in the Conference semifinals, Seattle faced off with the Dynamo in the Conference final. He scored once in the first leg while scoring and picking up an assist in the second leg to help the Sounders beat his former team 5–0 on aggregate and advance to MLS Cup 2017. Bruin played the full 90 minutes in the final as Seattle lost to Toronto FC 2–0.