Willoughby, 26, won his first start for NSW A against the Brumby Runners in Canberra earlier this year and is now in line for his first state cap.
The Waratahs will play four Tests against the Czech Republic, Romania, Romania A and Russia.
Kanaar has been banned for three months for stamping on the head of an opponent in a recent Toohey's New clash.
Willoughby was one of the mainstays of the Warringah pack this season, and was a member of the Shute Shield-winning team.
"Hugh is a genuine number eight with good skills at the line-out and with ball in hand," Waratahs coach Ewen McKenzie said in a statement.
"His size and skill levels complement the back rowers already selected, and he has the added benefit of being able to play both blindside flanker and lock.
"At 26, Hugh will be one of the older guys on tour, so this will be a great opportunity for him to show leadership despite being a debutant."
But the news was not so good for Eastwood flanker Hugh Perrett, who has been forced to withdraw from the shadow tour list because of injury.
Perrett suffered a compound dislocation of the finger in Eastwood's loss to Sydney University at the weekend and a decision on the fitness of injured Eastwood flanker Will Brame is expected on Monday.
Brame has been battling back and hamstring troubles in recent weeks.