Call JavaScript function present in HTML page from web browser in WPF

The easiest approach is to use WebBrowser.InvokeScript method:

 this.WebBrowser.InvokeScript("initialize", 1, 2);

Alternatively you could also rewrite you JavaScript code like this:

 function initialize(lat, log) {
    var mapProp = {
       center: new google.maps.LatLng(lat, log),
       zoom: 5,
       mapTypeId: google.maps.MapTypeId.ROADMAP
    };
    var map = new google.maps.Map(document.getElementById("googleMap"), mapProp);
 }

 document.myfunc = initialize; // expose it to the document scope

 google.maps.event.addDomListener(window, 'load', initialize);

So now you can access myfunc from C# code:

private void WebBrowser_OnLoadCompleted(object sender, NavigationEventArgs e)
{
    dynamic document = WebBrowser.Document;

    document.myfunc(1, 2);
}

You could also invoke myfunc without dynamic keyword:

private void WebBrowser_OnLoadCompleted(object sender, NavigationEventArgs e)
{    
   var document = this.WebBrowser.Document;

   document.GetType().InvokeMember("myfunc", BindingFlags.InvokeMethod, null, document, new object[] {1, 2});
}