I thought I'd jump on this thread to ask a follow-up question about a similar itinerary:

I'm flying YYZ-DTW-ICN-SIN in a couple of weeks. My YYZ-DTW is an A fare and the remaining legs are Z (It's all booked as a single ticket). I have no status with Delta but my fare class nets me lounge access. However, when I look up the list of available lounges in YYZ on Delta.com (with "Delta One Cabin Passenger" selected as the "Accessible for"), the only result is the KLM Lounge opposite Gate C32 in Terminal 3. There's a disclaimer that states, "Not Accessible To Passengers Departing On Canadian Domestic Or USA Transborder Flights".

So I'm perplexed: My YYZ-DTW flight is a "USA Transborder" flight so I think that means I won't have access in YYZ. But I'm continuing on to ICN after that so does that then qualify me for access?