I think it might depend on fare category. That's why I never buy Basic Economy. They have terrible restrictions on carry-ons and seat selection, for any airline.

For Standard Economy, as far as I know, you can always choose your seat for free when the check-in opens at 24 hours before departure. I did this as recently as one week ago on an AC domestic flight.

 

Interesting james…I’d been told otherwise, ie policy had changed for all categories.
i can’t seem to get any info on the AC site, so i emaied. Not holding my breath waiting fir a reply…

 

It would be great if others could comment. I did fly recently with AC, and just selected my seat (as normal) at check-in time. No cost for Standard economy.

But it's possible they may have changed something, recently.

 

They still allow it:

Within 24 hours of your flight:

Check in online or on your mobile device.

If you have not yet selected a seat, one will be assigned to you.
To change your assigned seat, choose from the remaining seats. A fee may apply depending on the seat you have selected and the fare you purchased.

 

Not very clear:,,,.a fee “may” apply….??

 

Depending on your fare class and preferred seat vs standard seat.