Once you have an SVG image loaded into an RsvgHandle, you can render it to a Cairo context any number of times, or to different Cairo contexts, as needed. As a convenience, you can pick a single element in the SVG by its "id" attribute and render only that element; this is so that sub-elements can be extracted conveniently out of a larger SVG.
Generally you should use
rsvg_handle_render_document() to render the
whole SVG document at any size you choose into a Cairo context.