As I’ve said before, Braavos is not a monolithic entity. So it may well be that the major institutions of Braavos have different reactions. Even there, there’s things that cut both ways.
The Faceless Men are probably the most militantly anti-slavery, but they were also the fiercest enemies of the dragonlords of Valyria, so that’s something of a tossup.
While the Iron Bank doesn’t deal in slaves, I’m guessing they probably lend to banks in the Free Cities who do (or whose customers do), so they probably would be the most bearish on helping Dany.
Likewise, the Sealord of Braavos might see anything that decreases the power of Volantis as a good thing, or he might blame Dany for tipping power over to the tigers after centuries of elephant rule.