Assigning specific apps to eSIM

Hi all,

I’m travelling abroad soon and looking to leverage an eSIM to increase my mobile data.

I’m wondering, when using an eSIM what happens to your WhatsApp? Would it work with my UK number still as it would be using data off a different phone number?

Within iOS is it also possible to assign certain apps to the eSIM to use data from, E.g. discord.

thanks!!