public Cursor Cursor {get; set;}

internal class CustomMapTool : MapTool
{
  public CustomMapTool()
  {
    IsSketchTool = true;
    SketchType = SketchGeometryType.Rectangle;
    SketchOutputMode = SketchOutputMode.Map;
    //A custom cursor file as an embedded resource
    var cursorEmbeddedResource = new Cursor(new MemoryStream(Resource1.red_cursor));
    //A built in system cursor
    var systemCursor = System.Windows.Input.Cursors.ArrowCD;
    //Set the "CustomMapTool's" Cursor property to either one of the cursors defined above
    Cursor = cursorEmbeddedResource;
    //or
    Cursor = systemCursor;
  }