People ask in forums online where to live in Montréal to learn French.
It matters little where you live in Montréal.
Furthermore, this is the wrong question.
The better question to ask is:
How will I spend my days?
Will you attend university in French? Will you accept work in French? Will you join a group where there are francophones? Will you share an apartment with a francophone?
There’s nothing preventing you from learning French in a typically non-francophone neighbourhood.
I have a Turkish friend who speaks fluent French. He never left Istanbul to learn French. He works in a hotel. He spends his days speaking with people.
It doesn’t matter that his neighbours speak Turkish. It doesn’t matter if your neighbours don’t speak French.
It may not even matter if your neighbours do in fact speak French. Just because there are francophones in your street doesn’t guarantee anything.
If you want francophone “atmosphere,” by all means, pick a typically francophone neighbourhood.
But don’t stop there, because what really matters is who you’ll spend your days with.
Focus on that instead if you’re serious about learning French in Montréal (or anywhere).