Sinner beat Zverev in a closely-contested final in Vienna six days ago, but the German was nowhere near his best in Paris.
Having saved two match points in a lengthy quarter-final win over Daniil Medvedev on Friday, Zverev looked fatigued from the first point.
He lost the opening set inside 30 minutes and did not hold serve until the first game of the second – and even then he had to save a break point.
Sinner was imperious though, hitting eight aces, winning 90% of first serve points and not facing a single break point.
He will bid for a fifth title of the year when he faces Auger-Aliassime, who earlier beat Alexander Bublik 7-6 (7-3) 6-4.
In the men’s doubles, Britain’s Henry Patten and Finnish partner Harri Heliovaara reached the final with a 6-3 6-4 win over French pair Quentin Halys and Pierre-Hugues Herbert.