Text rendering is done using Pango. The Pango::Layout object for printing should be created by calling the PrintContext::create_pango_layout() method. The PrintContext object also provides the page metrics, via get_width() and get_height(). The number of pages can be set with PrintOperation::set_n_pages(). To actually render the Pango text in on_draw_page, get a Cairo::Context with PrintContext::get_cairo_context() and show the Pango::LayoutLines that appear within the requested page number.
See an example of exactly how this can be done.