The FIA have just released a form in which they've announced that eight drivers will have a gearbox change in Canada, which is allowed as you're permitted one gearbox per six race weekend.
Both Ferrari's, Sergio Perez, Lance Stroll, Carlos Sainz, Fernando Alonso and Charles Leclerc are the ones who will have fresh gearboxes installed this weekend.
As for
Max Verstappen, he had a previous gearbox switch but has completed six race weekends since, meaning he's also not doing anything illegal. The exact reasons for the changing for each gearbox aren't known, but it undoubtedly has to do with reliability. Old gearboxes tend to be more prone to errors, like we saw with Nico Hulkenberg in FP1, whose gearbox got stuck in neutral.