I would recommend using your CI status. As a SkyTeam Elite Plus member, you'll get lounge access, SkyPriority benefits on the ground (e.g., check-in, security, boarding), free EC seating on YYZ-DTW, and a 50% discount on EC seating on DTW-ICN. As a DL Silver Medallion, you would only get free EC seating on YYZ-DTW at T-24 and a 25% discount on EC seating for DTW-ICN. Both statuses would provide the same extra checked bag.

The only advantage to using your DL FO status would be if you want to be eligible for complimentary upgrades or op-ups. But of course that advantage is moot if you replace your frequent flyer number with your AS status in the end.