Remote site archiving

I have an Exchange environment over three sites (2 sites with redundancy (6000 users split across Site 1 & Site 2) & 1 additional remote site (site 3 - 1000 users))

For EV, I’m proposing to design a centralised model, either at Site 1 or Site 2. However, in order to deploy this, I not sure how I would accommodate archiving mail for the 1000 users in site 3.

Thanks in Advance.

ASG Roger