There is no support for 64-bit DXI plugins. Many, probably most, of your 32-bit VST plugins should work.
Moving to a 64-bit Windows environment from 32-bit opens up more memory, from a 4 GB (about 3.3 GB usable) to now accessing roughly up to 192 GB of memory. In addition, each clock pulse processes twice the data 64 bits rather than 32 bits, which increases performance.
Several folks have also posted that they hear better sound quality in using the 64-bit plugins.
But to your original post, as I said above, most VST plugins should work just fine in 64-bit Sonar.
Bob Bone