I'd still place Base Trunks as a fair bit weaker than SS3 Boo Arc Goku, so it overall comes down to how you believe M8 Broly compares to Boo Arc SSJ Goku as well as whether we're basing the boost on his SSJ form or stacked on top of LSSJ. In the former case, SSJ Broly is at best somewhat stronger than CG SSJ Goku, so he gets beaten badly here. In the case of it stacking from LSSJ, it depends where you rate him. There's no official evidence on how he compares to Boo Arc SSJ Goku, FP Perfect Cell or the likes, though the fact Daizenshuu states his movie 10 SSJ self is stronger than SSJ Goku at the time and he's later shown stomping SS2 Gohan after his transformation does show the boost is significant enough that I doubt Galu's training gains outstrip such a gap. That said, I'd give it to Broly in that case.