Double click on the audio clip and press the Enable Stretching button that opens in the Loop Construction window. Next, change the Pitch at the top, click out of the control and hit the Preview button to hear the change.
SONAR 6, 7, 8 AND 8.5 Producer Edition offers much more powerful tools for manipulating audio in this way. See the AudioSnap and V-Vocal videos on the SONAR product page. Also check out this Audiosnap TechTip.