I first took the Year Start and End dates and used the Generate Rows tool to create every data between these two dates:

I then created a formula to create the Day column using datetimeformat([Days],"%A"). This gave me every day of the week, which I then filtered down to remove weekends.
The next step was to simply join the US and AUS holidays on the dates I had generated (left outer) and created a column of the US Holidays which I named Elf 2 to represent having two elves in two columns. I then joined the AUS Holidays and Robert's your father's brother.

Bonus - I simply summed the two columns, one for the US and one for the AUS business days, counting all the null values which would represent business days. Which gave me the following results:

