A FlyerTalk Posting Legend
Join Date: Sep 2012
Location: SFO
Programs: AC SE MM, BA Gold, SQ Silver, Bonvoy Tit LTG, Hyatt Glob, HH Diamond
Posts: 44,606
If you're flying all on AC metal, all that matters is the fare class.
When Google Flights deep links to AC, it sends a "cabin code" (B or E) for each fare, independent of the fare class for each segment.
When the fare class does not match the cabin code, you get the "________ is not available on this flight". As far as I can tell, that's the only thing the cabin code is used for.
It's not uncommon to see "J (Tango)" or "V (Business Class)" on AC's site. It's confusing, but as I said, as long as it's all AC metal, the only thing that matters is the fare class.
If you're really concerned, I'd just buy it and select seats (which is a pretty good indication of where you'll be sitting). If you don't like the result, you have 24 hours to cancel.