You will not be able to add a Guestbook or any of the Yahoo! Canada GeoCities Add-Ons from within Yahoo! PageWizards, however you may do this by opening the page in PageBuilder. PageBuilder is a more advanced page editing tool and may require more time and knowledge to learn how to use.
Also note that once you have opened and saved a file from within PageBuilder, you will not be able to open and edit that page with Yahoo! PageWizards again.