If I recall correctly every Sonar version past 6.0 updates the same VST scanner - it knows what version of Sonar calls it so there's no compatibility issues with it operating between Sonar versions (v6-X3).
What you probably need to do is to update the VST Scan Paths as seen by X2.
Each Sonar version keeps it's own set.
Open X2, open the Edit system menu go to Preferences, then check the VST Scan Paths under 'VST Settings'