Try calling CBSA and explain this is checked luggage that was in transit to US. They should be able to release to DL then. I'm betting KLM sent it onwards only to YVR and was thus sent to CBSA as an arriving package instead of connecting. Point out you were just connecting in YVR, and that this is a missing piece of luggage from that flight.

I had similar problems when flew to NZ last year. I took a weeks meds on plane with me, but checked the rest. Bags didn't come in with me. Filed claim, and three days later got call that the handling agent couldn't release my bags since I had meds listed. A call to NZ customs straightened it out. Since the luggage should have been with me at arrival, which would make meds allowable/exempt, they could release them.