Who would win in all-out-war: Canada or Australia?

Neither.
The Queen would command “cease this at once”, and Canada and Australia would respond: “of course, forgive us, your Majesty.”

Australia. More self-sufficient. Canada has the problem that they have a short growing season and could not supply all their food needs in the time they have to grow items.

Australia is, and can be, virtually self-sufficient.

The question is: What would they be fighting about?

What they would be fighting about is in the question.

Australia: wants an end to Canada’s curling and ”‘eh’”

Canada: no more kanagroos and reverse toilet bowl flushing

Canada.

Why?

Mounties.

I don’t know who would win. Politically they seem like mirror images. Geologically they are opposites. Both counties have about the same amount of people. I would expect a stalemate.

Depends on where it happens.
Either one would have a serious supply problem if they went to the other place.
But, Canada has a weak navy (decent Air Force, shitty Navy)
If they went there, Australian navy would shoot them out of the water, and they would not be able to maintain supply. If Australia came to Canada, they would own the sea lanes for supply.