Another vote for SMCalloutView. Check out my answer here for a quick start on implementing it.
Sorry to not actually answer your question per se, but Google's rendered UIView info windows are more hassle than they're worth, I think. You may be able to get a webview to load inside one of them, but the Maps SDK takes the custom UIView you set and then renders it into OpenGL, ignoring most (all?) updates you try to make.
Using SMCalloutView skips all of that and we put its view on top of the map, allowing you better control before and after drawing.