I found this answer on the Cakewalk Forum - It works a treat so I thought I'd post it here :)
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Guitar Sheet music is notated in Treble Clef but it's not true Treble Clef but rather an octave higher. You can have Sonar match regular guitar sheet music that you would buy in a store by...

Open Staff View Layout dialog box (right click in staff view and select Layout)
Under Staff Properties set Cleff = Octave-treble

No need to create a custom preset or set any transposition.
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