I flew YYC - KTM twice, the last time was AC YYC with connecting to Thai in HKG to BKK then BKK on Thai to KTM. Fares on TG seem much better on the Thai web site. BKK - KTM fares tend to be consistantly high on Thai sometimes it is about the same (or more) as HKG-BKK-KTM. The previous trip I got a very good fare on a multicity open jaw on the AC website going YYC_BKK returning DEL-YYC through London the DEL-London segment was in lattitude at about the same price as tango+ (seems to happen on multicity sometimes) , a seperate ticket BKK-KTM-DEL on Thai to BKK and Jet to DEL. The distance KTM to DEL is not great so you don't loose many miles. Cost for DEL-KTM-DEL on Jet is very low so you could also try flying to YYZ-DEL-YYZ on AC and codeshare Jet and a cheap tiicket on Jet DEL-KTM-DEL.
I am looking at the Air china option as a possibility for my next trip, I would like to try for a couple day stopover in Lhasa. The fares seem a bit high.