Fares will be slightly lower from YYC than YVR and you won't save anything by going through SEA once you add in the cost of getting there.
Choices from YYC (excluding Air Canada) are KLM, Lufthansa and British Airways. I'm not really enthusiastic about any of them but KLM has always treated me OK. In your situation I'd go talk to a travel agent; searching websites can be time-consuming if you're not used to doing it.