I would like to think that all my works have international reader-appeal, but I am originally from England, currently live in Australia and have two completed creative NF WW2 stories (a PB and an 8+/YA) that have English main characters, and a creative historical biography in progress that’s set in London. While they will be submitted to Australian publishers, I have a feeling that a UK publisher could well be most likely to make an offer. I also have five ‘normal’ picture book texts completed for any readership and one that is distinctively Australian. Would you advise attempting to partner with an Australian agent, one in the UK and one in the US? Do most US agents have co-agent partners in the UK for stories that will probably find a first home there, rather than for a sale of rights after initial release in America?
NO NO NO.
You don't want or need multiple agents.
You need ONE agent who will do multiple deals.
What you don't know is that the Australian publisher will most likely want the right to publish in English around the world. That's called "World English" That then means the Aussie publisher controls the rights for the UK and the US.
You wouldn't have anything for a UK or a US agent to sell. (An Australian publisher would generally not engage a US agent to sell rights; they'd do it directly.)
Whereas if you have ONE agent, they will strategize about which publisher is best suited for your work and which territory they're best suited to exploit.
World English has some very tricky aspects and you do not want to just assume that everything will work out.