I've recently started working on an updated and revised version of the entire GRN info thread, including the diplomacy of Gallia and the GRN. It won't be posted until it's done, so don't bother looking for it. I welcome some help from the community though - I've learnt my share of things in the time I've been here, but I'm far from being all-knowing when it comes to Discovery lore.
I looked through various faction info threads and wiki pages as a reference, and ran into contradictory and often outdated information. Some faction pages, a lot of them actually, are so outdated they don't even list a single Gallic faction in their diplomacy.
In this thread, I welcome statements, preferably but not necessarily from official factions, explaining their diplomacy with Gallia and its factions. For every faction of Sirius, especially about the less obvious ones, any information is appreciated. And while you're at it, update those diplomacy lists!