The second seed needed just an hour and seven minutes to see off his compatriot 6-1 6-4 in Washington on Sunday, ensuring he won the ATP 500 hard-court tournament without dropping a set.
Big-serving world number seven Raonic fired down nine aces and took four of the six break points he manufactured in the first ATP World Tour final between two Canadians in the Open era to secure the sixth title of his career.
The 23-year-old Wimbledon semi-finalist wasted no time in getting the upper hand as he won the first three points of the match on 13th seed Pospisil's serve and claimed an immediate break.
World number 36 Pospisil had a chance to break back straight away, but Raonic stood firm.
Although Pospisil got on the board to make it 2-1, there was no way back for him as the favourite reeled off the next four games to win an ominously one-sided first set.
The second set was more closely contested as it went with serve, with Pospisil winning 87 per cent of points on his first serve and Raonic successful with 93 per cent of his first-serve points.
The countrymen looked destined for a tie-break until Raonic put his compatriot under pressure when leading 5-4 and took the only break point of the set to end his wait for a first title in 2014 - his previous success coming in Bangkok last September.