I've found out the solution! Thanks to Firebug ;)
//"markers" is an array that I declared which contains all the marker of the map
//"i" is the index of the marker in the array that I want to trigger the OnClick event
//V2 version is:
GEvent.trigger(markers[i], 'click');
//V3 version is:
google.maps.event.trigger(markers[i], 'click');