the signaling protocol depends on the specific solution:
for Ethernet over MPLS pseudowire the VC label is provided by LDP ( targeted LDP session that means an LDP session between two devices not directly connected to each other)
For VPLS there are three options:
VPLS with manual neighbors configured on each PE -> difficult to manage when adding a new site all other need to be configured.
VPLS with MP BGP auto discovery: using route targets and a specific address family each PE can dynamically discover those neighbors in the same VPLS (using the same route-target) and then use targeted LDP to build pseudowire to each of them
VPLS with MP BGP and MP BGP for auto discovery: in this case a different sub address family is used the PE nodes are discovered using MP BGP and MP BGP is used also to allocate blocks of MPLS labels to be used by remote PE when sending to the local PE node. (here there is the important concept of site id).
Finally in EVPN another MP BGP address family is used. To be noted a true route exchange happens only on EVPN where MAC addresses or MAC addresses and IP addresses can be advertised. In VPLS the MAC address learning is still driven by traffic like in a conventional switch. So EVPN have superior control over unknown unicast it does not need to flood to all sites an unknown destination MAC address.