Roy and the Blues had agreed to terms on Saturday.
The 30-year-old Ottawa native split last season between Dallas and Vancouver. He had four goals and 18 assists in 30 games with the Stars before the Canucks acquired him at the trade deadline for defenceman Kevin Connauton and a second-round pick.
Roy was seen as a boost to the Canucks' injury-riddled second line. he had three goals and three assists in 12 regular-season games for Vancouver, but managed only one assist in the playoffs as the Canucks were swept by San Jose.
The five-foot-nine, 184-pound forward has appeared has 168 goals and 287 assists in 591 games with Buffalo, Dallas and Vancouver.
His best offensive season was 2007-08, when he had 32 goals and 49 assists in 78 games.