We'll find out this year. From what I've heard, he's eligible for salary arbitration, though we retain exclusive rights. He should get a fat contract, though no right to change teams.
According to mlb4u.com which gets its info from the offical team media guides, Patterson's service time after this season will only be 2 years 126 days. 3 full years is required for arbitration.
Patterson's only shot at arbitration is if he falls into the eligible "Super-Two" group. This can not be determined until season's end. The players within the top 17% longest service of the total "Super-Two" group become eligible for arbitration.
Don't forget, he was the Expos #1 Draft pick, #5 overall in 1996.