There is no land-based halfway point between Toronto, Canada and Brisbane, Australia. The Pacific Ocean separates them entirely—approximately 14,500 km (9,000 miles) of open water.
Any "midpoint" would fall in the central Pacific, thousands of kilometers from the nearest land (perhaps near the Line Islands or Phoenix Islands).
Travel options:
No roads, no ferries, no islands with regular transport at the midpoint. It's a purely aerial or maritime connection.