My understanding is that an ambassador is considered to be a representative sent from one head of state to another; an ambassador to the United States for example presents his credentials to the President not to Congress or to the nation at large.
How does this work between the United Kingdom and Canada (or Australia, New Zealand, Jamaica, etc)? While these countries have different governments their heads of state are all one person - Queen Elizabeth II. Wouldn’t Her Majesty effectively be sending an ambassador to herself? Does she just go ahead and send her ambassador to the Governor General who accepts the ambassador on her behalf? Or is there some alternative form of diplomatic representation between these countries?
While the Queen is the titular Head of State of Australia, when not in the country the Governor-General stands in for her and is essentially the HoS. So Australia’s ambassaor to England is his representative.
Countries where the Queen is the head of state don’t send ambassadors to each other. They send High Commissioners. So one speaks of Australia’s High Commissioner to New Zealand, or to Canada, or to the UK etc.
Not just Commonwealth Realms, but Commonwealth Republics too. For historical reasons members of the Commonwealth of Nations exchange High Commisioners. They have diplomatic relations between their governments, not their heads of state. In some countries even have Commisioners instead of Consuls.