If two armies arriving on the same day, which one is attacking/defending?

Solution 1:

If they both arrived at the same time, the defending party goes to whoever is controlling the province at the time, and that would be you correct?

Happy to help :)

Solution 2:

It goes through the country in order by their tag, following this list (https://eu4.paradoxwikis.com/Countries)

EG. If France and England are fighting each other and their two armies will both arrive on the 19th of may, England will be defending and France will be attacking because England (43) will arrive at the province first and France (106) will arrive second.

Note that Rebels Pirates and Natives are first, and the Roman Empire and special countries are last.