If you're currently in the United States, traveling to Canada, Mexico, or the Caribbean will not allow you to stay longer in the USA. According to the US embassy in Australia.
You cannot extend the time on the Visa Waiver Program. The 90 days also includes any time spent in Canada, Mexico and adjacent Islands. Therefore, you cannot cross the border into these areas and then return for another 90 days.
Adjacent islands are defined according to ICE as
- Saint Pierre
- The Dominican Republic
- The Bahamas
- The Windward and Leeward Islands
- Other British, French, and Netherlands territory or possessions in or bordering on the Caribbean Sea
Your best bet would be to return to Australia or visit a country on another continent. However, you would not be guaranteed entry back into the United States and you will likely be questioned about returning to the US so soon.
If you stayed more than 90 days in the first place, your ESTA would be revoked and you would need to apply for a visitor visa. It may be challenging to prove that you will not overstay in the future.