Answered question
Can’t acces internet mobile data in Montreal but my friends with fizz can , wtf ?
Double check that you have the right APN settings. You can find the current settings at https://fizz.ca/en/faq/what-are-fizz-network-settings-apn.
Also, enable roaming if it's off. It doesn't make sense, I know, but it seems to work. I recall needing it enabled when I visited Québec City earlier this summer in order for Internet to work consistently.
Other answers
Avez vous esseyez de mettre le téléphone an airplan mode pour 20 seconds?
Avez vous esseyez le truc de mettre le téléphone an airplan mode pour 20 seconds?
If airplane mode doesn't work you may want to restart your device or check to make sure 3g/4g is enabled.