As mentioned upthread, here's the official update from AC:
Baggage Through-Check on Separate Tickets

As per IATA recommendations, Air Canada will follow suit with our airline partners and, effective immediately, we will no longer offer the ability to through-check customers and/or baggage to the destinations of the second ticket, except in the following scenarios: - Purchase individual Air Canada (014) tickets.
- Purchase individual tickets from Pacific Coast (8P) or Air North (4N)
- An approved and documented regulatory or legal exception on the customer's file
- During irregular operations, two tickets were issued as a result of a single coupon reissue (including Air Canada to Other Airlines)
- For instance, a customer may have an original YUL-AC-YYZ-LH-FRA ticket that has been reissued due to IROP on two tickets: YUL-AC-YYZ on AC (014) and YYZ-LH-FRA single coupon reissued on LH (220).
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