To watch the show live, you would have to use a VPN that has strong Australian servers. In addition to that, you would also have to subscribe to the Australian channels that are going to broadcast it live.
For that, there are several paid channels, but Network 10 and Racing.com are the only two that will be broadcasting the event for free. You can download and install ExpressVPN and then connect it to an Australian server simultaneously to catch the Melbourne Cup Live.