Precious Achiuwa, who was listed as questionable on Tuesday, will also be in the lineup.
Anunoby hasn't played since Nov. 15 due to an injured left hip pointer. Birch is dealing with a lingering knee issue that is a matter of wear-and-tear, with swelling going up and down over a course of weeks, according to Sportsnet's Blake Murphy. The Montreal native missed a week with the same injury earlier this month.
Watanabe has yet to play this season after suffering a calf strain in the pre-season. The 27-year-old from Kagawa, Japan averaged 4.4 points while playing 14.5 minutes per game with Raptors last season.