P/Invoke使わないで モニタハンドラを取得してみた ref: http://qiita.com/yu_ka1984/items/4a0439d421593c763fc4

file0.cs

var monitorfield = typeof(System.Windows.Forms.Screen).GetTypeInfo().DeclaredFields.Single(x => x.Name == "hmonitor");
var Screens = System.Windows.Forms.Screen.AllScreens.Select(x => new {
                            Screen = x,
                            hmonitor = (IntPtr)monitorfield.GetValue(x) });