How are Religious Temples chosen for the provinces?

[Arjos]

We actually selected, when possible (that is archaeology or sources telling us), the most important cult for each province...

Then again it is also very difficult (really futile) to determine a single deity over others. Especially since the traditions of the time had several deities equally as important, or with varying importance throughout the year (festivals and seasons)...
Historically there often were also cultures, like say the Romani or the people of Nesha (Hittites) it was customary to bring all the cults to the capital and their chief places of worship developing there...

Even modding two temples per province (which forces one tier to be always just at level 1) is not an optimal representation...

Another problem, of course, is that within a single province there were more than one main place of worship. So ultimately we had to pick those at the political centers or very important regional ones...