Huskies (1-0) quarterback Jesse Mills went 8-for-16 and threw 109 yards for two touchdowns and no interceptions.
Ryan Tremblay caught two TDs and Brett Lauther kicked three field goals on five attempts.
The Mounties (0-1) opened up a 14-2 lead in the second quarter after Nick Kukkonen plunged in for a TD to open the scoring 7:06 and Donovan Saunders picked off Mills and ran 62 yards for a major at 1:58.
Lauther kicked a field goal from 41 yards out to cut the lead to 14-5 heading into intermission.
Elswhere in CIS football, it was: No. 8 Sherbrooke 39, McGill 13; No. 5 Saskatchewan 33, Regina 10; and No. 4 Calgary 30, No. 10 UBC 25.
At Halifax, Saint Mary's came out blazing in the third quarter as Nick Kukkonen recovered a fumble at the Mounties 6, leading to Leger's first touchdown of the game at 13:34.
Under two minutes later Mills hit Tremblay with a 15-yard TD pass and Lauther booted a rouge point to put the Huskies ahead 20-14 at 9:58.
Tremblay made it 27-14 five minutes later when he caught a 20-yard touchdown pass from Mills.
Leger ran in his second at 2:38 for a 34-14 lead before Bryce Fisher opened the fourth quarter with a 15-yard TD interception return to put the game out of reach.
Lauther kicked two more field goals and a rouge and Melvin Abankwah ran in a TD from 12 yards out in the dying second to complete the rout.
No. 8 Vert & Or 39, Redmen 13
At Montreal, Jeremi Doyon-Roch threw a 362 yards for two touchdowns to give Sherbrooke its second straight win.
J-C. Beaulieu rushed 20 yards for two TDs while Simon Charbonneau-Campeau and Ismael M-Bamba each caught a major for the Vert & Or (2-0).
Alex Hutchison returned a fumble 41 yards for a Redmen (0-2) touchdown and Austin Anderson kicked two field goals.
No. 5 Huskies 33, Rams 10
At Saskatoon, Jahlani Gilbert-Knorren went 16-for-32 and threw 358 yards for two touchdowns as Saskatchewan won its second straight with a victory over its provincial rivals.
Gilbert-Knorren hit Dexter Janke with a 101-yard TD pass in the second quarter to tie the game at 10. Janke also had a major in the fourth quarter.
Garrett Bolen caught a touchdown pass from 12 yards out and Stephen McDonald kicked three field goals for the Huskies (2-0).
Austin Bates had TD fumble return for Regina (0-2).
No. 4 Dinos 30, No. 10 Thunderbirds 25
At Calgary, Steven Lumbala ran in a nine-yard touchdown with 18 seconds left to play to lift the Dinos over the University of British Columbia.
Lumbala rushed for a total of 204 yards and two TDs, including a 16-yard drive in the third quarter.
Eric Dzwilewski threw 212 yards and one touchdown for the Dinos (2-0).
Quarterback Billy Greene was spectacular for the Thunderbirds (1-1), throwing 255 yards for three touchdowns.