Serge Ibaka added 25 points and nine rebounds, Fred VanVleet had 21 points, and Danny Green 12 points and nine rebounds, The Associated Press reported.
The Raptors slowly took charge in the second and third quarters and withstood the Bucks' comeback attempt in the fourth.
Giannis Antetokounmpo had 43 points and 18 rebounds for Milwaukee. Malcolm Brogdon added 15 points, and Khris Middleton and Eric Bledsoe each had 14. The Bucks had won five straight.
Milwaukee was coming off a 144-112 victory over Atlanta on Friday night, while Toronto had a day to rest following a 125-107 loss to the Spurs on Thursday night in Leonard's return to San Antonio.
The Raptors put it away with a 15-2 run, taking a 110-98 lead on Siakam's wide-open triple from the corner with 5:14 to play.
Trailing by as much as 13, the Bucks opened the fourth quarter with a 14-4 run, capped by Antetokounmpo's layup and three-pointer, and led 96-95 with 8:12 left.
Kings 123 Warriors 127
Stephen Curry scored 20 of his 42 points in the fourth quarter and had 10 three-pointers, and the Golden State Warriors held on to beat the Sacramento Kings 127-123 on Saturday night.
Kevin Durant added 29 points, nine assists and five rebounds, and Klay Thompson scored 20 points to help the Warriors complete a three-game sweep of the season series.
The three games were decided by a total of 10 points.
Coming off a 135-134 overtime loss to Houston on Thursday night when they let a 20-point lead slip away, the Warriors blew another big lead in the third quarter before storming past the Kings over the final 12 minutes.
Curry led the way with five of his triples in the fourth, and had a pair of key three-point plays. Curry also closed out the quarter with a pair of free throws with 9.4 seconds left.
Buddy Hield scored 32 points on a career-high eight 3s for Sacramento. The teams combined for an NBA-record 41 three-pointers, and the Kings set a franchise record with 20.
Justin Jackson added a career-high 28 points, and Willie Cauley-Stein had 14 points and 13 rebounds.