This might work for you, although you have to buy a separate ticket for the LAS trip and you will have an open jaw in the DTW/ORD area.
HKG-SFO-NYC-DTW open jaw YYZ-LHR-HKG.
Having lived in E. Lansing many years ago, DTW is about equal distance from Chicago and Toronto. Comes to about 19850 miles for the flight segments and gets your transcon on AA.