Similar situation happened to me on Monday. My morning flight YYZ to CVG was cancelled due to "Crew Sleep", and I was rebooked thru DTW to PHX. My DTW-PHX leg was the dreaded "seat request" card, so I called up the DM line to see if they could help.

It took a little prodding, but after I mentioned that I had been in F on the original flight, the agent was able to "unlock" (her term) the wait list or upgrade list that by now was under the control of the DTW GA. Confirmed my upgrade while I was on the phone, total call time under 3 minutes.