Ran into the same issue since I use Tonic as well. If you still have 6/6.5 installed, you can simply copy the files as follows if using Windows 7:
Copy C:\Program Files\Steinberg\Cubase 6\VSTPlugins\Filter\Tonic.* to C:\Program Files\Steinberg\Cubase 7\VSTPlugins\Filter
Or if you intend to keep 6.5 installed, point the VST 2.x Plugin Path to C:\Program Files\Steinberg\Cubase 6\VSTPlugins\ from Devices > Plug-in Information.
Mark