Maybe try something like CommandToClient('canvas.pushDialog','nameOfCrossHairGui');
That would attempt to trigger
clientCmdcanvas.pushDialog, which doesn't exist by default nor can exist due to being an invalid name for a function.
Seondly, the crosshair is not a GUI (well, dialog- it's still a GUI
control); it's an object in the center of the
PlayGUI that is set to being visible or not.