m.y

Aeroplan award routing is limited by some distance based on city pairs. From YVR, UA hubs tend to be far south of YVR so flying via UA hubs would add quite a bit of distance that would likely invalidate the routing.

Example for YVR-LHR:

Nonstop is 4723 miles

via DEN is 5784 miles (+22%) DEN is 1114 miles from YVR, significant backtrack

via SFO is 6167 miles (+30%), closer than DEN at 800 miles, but totally backtrack

http://www.gcmap.com/mapui?P=yvr-lhr...hr,yvr-sfo-lhr

I don't know what the distance limit between YVR and LHR is, but flying UA hubs will increase the chance of you breaching the limit.

The issue isn't as severe for YYZ since UA hubs of ORD and EWR are much closer, less than 500 miles away. EWR also involves much less backtracking, adding only 7% comparing to nonstop YYZ-LHR distance.