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You can geo-target the AU and US subdomain to the respective countries, but you can't target the EU as it isn't a country. HREFLANG can help as well, it depends on the differences in the content. You can do both, but in terms of what you should do: HREFLANG = regional language changes (US English vs AU English) Geo-Targeting = content changed to target that specific country (ex. products sold in the US but not AU, or extra regulatory content due to a country's laws OR (and a better example) the content needs to be different because selling your product in AU vs US is different like Christmas cards in each country, one has Christmas in summer and the other in winter).