What you want to do is create a network layer. This layer will allow you to use the same WebClient for what ever you want.
For example:
public static class NetworkLayer{
public static WebClient wc;
public void InitializeWebClient(){
wc = new WebClient();
}
public void MakeCall(Uri uri){
if(!wc.isBusy){
wc.DownloadStringCompleted += (s,a)=>
{
//Get your results
};
wc.DownloadStringAsync(uri);
}
}
}
MainPage.XAML.cs would reference your network layer
NetworkLayer.Initialize();
NetworkLayer.MakeCall(new Uri("http://www.google.com",UriKind.RelativeOrAbsolute));