I guess you're using a placeholder and rendering the content inside that, so a fixed 'page' size.
Yep, add a placeholder in Xara with a special tag {page_content} and this is where the CMS will output content onto the page. For Xara yes a fixed page size by default but you can adjust this manually to suit or there's a javascript tweak that allows the page to extend and accomodate the dynamic content automatically.