A custom WireGuard VPN service or client that switches traffic via different servers dynamically

I want to create a simple web service that'll manage WireGuard VPN servers of mine in defferent locations. It'll work like this: whenever I try to access a site in from certain, pre-defined list, a web service (a) or a local customly-modified VPN client (b) will switch me to a VPN server in a certain location. When I go back to other, normal website, it'll switch me back to the last VPN server.

How would I go about this? Will it be implemented on the side of the server (a) - web service? Or on the client one (b) -- by a custom VPN client which I'd have to modify to incorporate this functionality?