CAAC network is an example of how bilateral relations can develop into more formal, tight and multidimentsional relations. When building the networks, the first target member cities were those twinned with the West French ones. This trend continues in the present, as twinning is an awesome first door for cities when it comes to International Relations.
Non exhaustively, some of the twinnings that are highlighted by CAAC, or were at the time of its foundation are:
Rennes with Santiago de Compostela, Exeter and Cork
Gijón and Niort
Avilés and Saint Nazaire.
Cardiff and Nantes.