You'll need to turn data roaming "ON" in your phone's settings, to access data in Canada and/or Mexico. Remember to turn data roaming "OFF" when you leave Canada and/or Mexico or if you insert your Australian sim card into your phone.
Only the USA, Canada and Mexico Extreme Plan with data works in Canada and/or Mexico.
You won't be able to access data on the USA Max Plan, USA Saver Plan, USA Daily Plan or USA Budget Plan.