If you're flying between SGN in Vietnam and YVR in Canada, there're several decent options on Star Alliance.

1. YVR to NRT (Air Canada) and NRT to SGN (ANA)
2. YVR to ICN (Air Canada) and ICN to SGN (Asiana)
3. YVR to SFO (Air Canada) and SFO to SGN (United) - one stop in HKG
4. YVR to PVG (Air Canada) and PVG to SGN (Shanghai) - this might not work in the future depending on whether Shanghai will leave Star Alliance

from YVR to WAW the obvious choice would be either LH or UA (with a stop in Chicago and ongoing with LO)

for the status issue, you can try to have a status match into a star alliance program, so you can have access to lounges (if you are matched to gold) and continue to accumulate with Aeroplan.

If you also consider award travel, I have found seats relatively easy to get on LO from Chicago ORD to WAW in Business Class. They seem to offer very decent amount of award seats on that route.