The second set was a tighter battle as Pospisil raised his game before Raonic delivered the knockout blow in the 10th game for his sixth ATP title, his first of the year.
Raonic, 23, playing his first event since making the Wimbledon semi-finals, is projected to rise from seventh to sixth in the ATP rankings.
"I couldn’t have imagined starting that well," Raonic told ESPN.
"It’s tough after a few weeks away. I couldn’t have asked for a better way to lead into probably my most enjoyable part of the year."
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Pospisil, who won a tough three-set semi-final against Frenchman Richard Gasquet late on Saturday, was flat at the start of the final.
"He came out so strong. He really caught me off guard," said the 13th seed, who is still seeking his first ATP title.
"I wasn’t 100 percent but nobody’s 100 percent at this stage. Everybody's dealing with something. I didn't sleep much last night.
"I don’t think it would have made much difference to be honest, especially that first set."
Raonic's lethal weapon was his dominating serve. He dropped only two points on first serve, one in each set.
The second set was closer as Pospisil's serve improved.
Raonic finally broke serve on match point, firing a backhand crosscourt passing shot for the winner.
Next up for both players is a home game or sorts, the Rogers Cup starting in Toronto on Monday.
In the women's final, sixth seed Svetlana Kuznetsova of Russia beat Kurumi Nara of Japan 6-3 4-6 6-4 in a match that stretched over two hours.
Kuznetsova broke Nara's serve five times but was broken herself on three occasions.
(Reporting by Andrew Both in Cary, North Carolina; editing by Martyn Herman and Gene Cherry)
