You could use the standard IE's print feature (through the ExecWB method), like this:

public partial class PrintWindow : Window
{
    public PrintWindow()
    {
        InitializeComponent();
        webBrowser.Navigate("http://www.google.com");
    }

    // I have added a button to demonstrate
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        // NOTE: this works only when the document as been loaded
        IOleServiceProvider sp = webBrowser.Document as IOleServiceProvider;
        if (sp != null)
        {
            Guid IID_IWebBrowserApp = new Guid("0002DF05-0000-0000-C000-000000000046");
            Guid IID_IWebBrowser2 = new Guid("D30C1661-CDAF-11d0-8A3E-00C04FC9E26E");
            const int OLECMDID_PRINT = 6;
            const int OLECMDEXECOPT_DONTPROMPTUSER = 2;

            dynamic wb; // will be of IWebBrowser2 type, but dynamic is cool
            sp.QueryService(IID_IWebBrowserApp, IID_IWebBrowser2, out wb);
            if (wb != null)
            {
                // note: this will send to the default printer, if any
                wb.ExecWB(OLECMDID_PRINT, OLECMDEXECOPT_DONTPROMPTUSER, null, null);
            }
        }
    }

    [ComImport, Guid("6D5140C1-7436-11CE-8034-00AA006009FA"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    private interface IOleServiceProvider
    {
        [PreserveSig]
        int QueryService([MarshalAs(UnmanagedType.LPStruct)] Guid guidService, [MarshalAs(UnmanagedType.LPStruct)]  Guid riid, [MarshalAs(UnmanagedType.IDispatch)] out object ppvObject);
    }
}