It sounds like your issue is with AS rather than DL, although Canada might have different consumer protection rules than the USA.

I'm assuming DOT rules apply and this was an IDB where the airline didn't give you a statement of your rights and didn't ask for volunteers. Moreover, it's not clear whether AS followed their own priority rules (that must be stated in their CoC) to select the passengers to be given IDBs. It sounds like you weren't the last to check in and you had seat assignments if you were given boarding passes (is this right or did you have seat request cards or whatever term AS uses for the thing to get you through security when the seat will be assigned at the gate), so perhaps you were picked because you had award tickets or were viewed as DL passengers (since DL miles were used and DL had transferred the ticket and reservation over to AS). These might not be the criteria specified is AS's own rules in its CoC.