As we all know (and as I experienced as a boy living in Canada), a new flag was adopted. Frankly, I hope the Aussies make the change.
The Canadian situation is a bit different from the Australian though. The red ensign you've displayed was never actually an official Canadian flag. It was a commonly used one but it did not have the status of a National Flag in law (it had status as a Naval Ensign by order of the Admiralty, and the Canadian government encouraged its use in cases where a distinction between Britain and Canada was needed). Until 1965, the only official flag of Canada remained the Union Flag of Great Britain and Northern Ireland. While Canadians did fight under the Red Ensign during both World Wars, and in Korea and other smaller conflicts, it was not a National Flag.
In Australia, our current flag was accepted as official in 1903, only two years after Australia became a separate nation. We fought wars under it from 1901 onwards.
There's certainly no reason Canada should not have made the change it did - as a sovereign nation that is its right, and it may well have been the right change for Canada. But I do not think a similar change is warranted here.