The 23-year-old American finished at 6-under-par 274, three strokes clear of overnight co-leader Michael Harris, who stumbled to a 4-over 74 in windy conditions.
'It means so much to win,' said Tomasulo, who collected $24,000 for the victory. 'This tour always has great fields, so to get a win under my belt is huge for my confidence.'
Rob Oppenheim was one of just five players to score in red numbers during the final round, and he ended alone in third place at 1-under-par 279 after shooting a 68.
Stephen Gangluff and Chris Greenwood shared fourth place at 2-over-par 282, while Kevin Senecal, Wes Heffernan and Anders Hultman tied for sixth one stroke further back. Those five players averaged nearly three strokes over par on the day at Club de golf de L'ile de Montreal.
Tomasulo, who held at least a share of the lead after Friday and Saturday, was a little better in his final round. He gave himself the outright lead with an eagle at the par-5 second, which Harris bogeyed to fall three shots off the pace.
Harris lost two more strokes from his score with bogeys at Nos. 5 and 8, but he was within two after Tomasulo bogeyed three straight holes from he eighth.
However, Tomasulo followed with a birdie at the par-4 11th, while Harris bogeyed the hole to fall four shots off the pace. Tomasulo then played his final seven holes at plus-1 to remain ahead.
'That was the toughest day by far,' said Tomasulo. 'For a while, it wasn't looking too good, but I bounced back. This was my first time with the lead going into the final round, so I'm glad I was able to close it.'
Tomasulo has finished in the top-six in five of his nine Canadian Tour starts.
But his success comes as no surprise -- winning is in his background. In 2004, he was named a First-Team All-American, while he captained the University of California's NCAA Championship team.
'That was the goal this year -- to win and try to get into one of those top two spots on the money list,' said Tomasulo.
Brad Fritsch (69) and Jaime Gomez (73) tied for ninth place at 4-over-par 284. First-round leader Ben Bunny shot a 1-over 71 and led a group of four golfers knotted one stroke further back in 11th place.