Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Dumaguete City to Montreal as you normally would.
For a flight from Dumaguete City to Montreal, you will be flying from Dumaguete. Dumaguete City (DGT) is just 3.0 km from the center of the city. Dumaguete is the only Dumaguete City airport and it handles 0 outbound flights to Montreal per day. 0 airlines have flights to Montreal from Dumaguete City on a regular basis.