Australia - following colonization and, later, subsidised immigration - was largely British.
Australian were British subjects until late last century.
Even back in the nineteen fifties Australia self-consciously emulated American trends.
Not as much as they did the British from which in many aspects they were indistinguishable.
Now it's trendy to despise US trends, while voraciously devouring American culture at every opportunity.
Really? I'd have thought that would depend on your politics.
In fact, Australia is about as multicultural as you can get.

You mean we have a settlement policy foisted on us by a handful of pollies and lobbyists called multiculturalism.
Where once there were few restaurants and the greasy cafes served exclusively British food, immigrants other than British have provided a glorious array of wonderful restaurants and supermarket stocks from all over the world.
I like roast lamb peas and mashed potatoes thanks and don't find them greasy at all. Restaurants and food does not make a country Multicultural. Most food eaten in Australia is grown in Australia. Recipes can be bought in books.
If MacDonalds, KFC and so on are in most suburbs, they're overwhelmed by Thai, Vietnamese, Chinese, Japanese, Indonesian, Russian, Italian, French, Spanish, Turkish, Greek, Indian...the list is endless...restaurants and takeaways.
Yet enclaves tend to satisfy mainly one nationality and their cuisine. Enclaves are signs of disunity.
Australians pick up US idioms, but they've always picked up on other languages and colloquialisms; it's what the English language does. Americans owe a large part of their accent to the Irish, and all of their language to European and New World and other sources.
Australians used to be fairly good mimicks. So what? We have quite an extensive home grown linguistic idiom called STRINE.
If any Australian would prefer to avoid American language and culture, they're free to do so. It isn't compulsory.
And apart from the upturn due to Filipino Immigration where they were indoctrinated due to Clarke AFBase etc the American influence was rather mild. Even considering the Musical and Cinematic influences of America globally.