Leading 47-46 at halftime, Canisius pulled ahead 57-48 after Robertson's back-to-back 3s and a jumper by Crumpton.
Khallid Hart scored 13-straight points and Connor McClenaghan's dunk pulled Marist within 76-70 with 2:39 left. Kristinn Palsson hit back-to-back 3s to pull the Red Foxes within five points, but McMillan sealed it with four free throws in the final 15 seconds.
Robertson and McMillan combined to shoot 13 for 13 from the free-throw line and Canisius was 27 of 34 from the stripe.
Hart led Marist (4-8, 1-2) with 26 points and six 3s. Palsson had 18 points on six 3s, both career highs.