Just to expand a bit on what's already been posted: Rewire is an audio link; it will get the audio generated by score-driven instruments hosted in the notation program back into SONAR for realtime playback and recording in sync with SONAR's clock. But it won't allow you to have the score drive instruments hosted by SONAR or facilitate transferring the MIDI to SONAR.
I also use Notion, but not extensively. It has its own orchestral sounds and can use any VSTs you have that are available to all hosts. But if you want to work with the MIDI in SONAR, you'll eventually have to export/import MIDI or XML.
Incidentally, my main issue with Notion is that it's limited to 44.1kHz, and I've been running SONAR at 48kHz for a long time now which makes it inconvenient to work with Notion.