Air Canada introduced "branded fares" several years ago. See this thread for more discussion:
Branded Fares (2019 onwards)

The quick summary is that the fare class (the single letter - B, M, U, H, Q, etc) is not a reliable indicator of the fare brand that you've bought.

The Air Canada fare brands (https://www.aircanada.com/ca/en/aco/...-and-fees.html) - Standard, Flex, Comfort, Latitude - can each be sold using many different fare classes. Thus it's quite possible for a U class fare for one ticket to be a Flex fare brand, while another ticket on the same plane has a U class ticket which bought a Comfort fare brand.

Bottom line, in almost all cases it's the fare brand (the name) that you care about, and which determines the features of your ticket. Also, with a handful of exceptions, the fare class (the letter) will not tell what the purchased fare brand was. You need to look at the fare basis code (which looks like this: LAAEROTG) to tell you what the fare brand is.

Questions and more discussion on that topic should go in the branded fare thread.