Have a pretty complex 20 hour delay that I'm trying to figure out how to go about. I have a claim open with Lufthansa under the EU/261 regulations since they are the original reason I got delayed. If they deny it I'm trying to figure out if Air Canada might be on the hook for compensation for the delay that occurred in YUL.

Original itinerary
Dec 25 GOT - FRA Operated by Lufthansa (delayed which caused me to miss my connection to YYZ)
Dec 25 FRA - YYZ Operated by Air Canada
Dec 25 YYZ - YQB Operated by Air Canada

New itinerary:
Dec 25 GOT - FRA Operated by Lufthansa
Dec 26 FRA - YUL Operated by Air Canada
Dec 26 YUL - YQB Operated by Air Canada (original departure 1pm, rebooked to 5pm)

1. FRA - YUL is delayed by 29 minutes and I exit the plane at 12:25pm
2. My 1:00pm connection to YQB has been automatically rebooked to the 5:00pm departure while I'm in the air
3. At 12:35pm I get to the gate of my original YUL - YQB flight for which I still have my boarding pass
4. Gate agent denied boarding since I have checked luggage
5. 17:00 EST departure for which I'm rebooked to ends up being delayed and I get to YQB at 18:43 EST

If Lufthansa denies my EU/261 claim the delays caused by Air Canada in YUL would fall into the 3 hours or more but less than 6 hour bucket worth 400$.