Hanoi is 11 hours ahead of Montreal
There is no standard 8-to-6 overlap. Someone joins early or late.
Montreal and Hanoi are 11 hours apart, and that gap is wide enough that their normal 9-to-5 workdays never quite touch. If you meet regularly, fix one off-hours slot and rotate it between Montreal and Hanoi so the burden doesn't fall on one team. Because Montreal and Hanoi don't both observe daylight saving, plan to re-check the overlap around March and November.