I'm not in front of my DAW, however from memory, I believe Sonar only scans for plugs in the paths you've configured. I believe it can be configured under preferences - VST settings (or something similar to that).
Make sure whatever path you think BFD may be installed to is included in the list of scanning paths you see.
You then either manually scan for plugins to see if Sonar now finds it, or you can select to have Sonar automatically scan for plugins everytime it starts.
Hope that helps.
Russ