Hey, how are you?, for this kinda of project I would utilize different channels to test the results, of course that we can create some automations to invite french speakers from Linkedin, Discord and Reddit, but everything depends of the public that you want, just french speakers? no age, gender, role, location? if so, on the top of my head Im thinking in a lot of channels, like people who have completed more than 70% of the french course on duolingo (example)
We can talk more if you want to procede o/ let me know.