Either have Sonar include the VST Plugins folder located in the Native Instruments/Kontakt 3 folder in it's plugin scan.
Or move the .dll files from Native Instruments/Kontakt 3/VST Plugins folder to the Cakewalk/Sonar 8/VST Plugins folder.
Not sure about GVI, probably the same way as well.
It's just a matter of Sonar knowing where they are.
If the .dll files (vst files) are in the Sonar 8 VST Plugins folder, Sonar automatically scans in the new vst files, otherwise you'll have to direct Sonar to scan in the other locations or move them to the Sonar 8 VST plugin folder.
hope this makes sense - It's easier done than said