I'd say definitely do business class. I've done both on flights to SEA and it's a world of difference.

If you don't have too much flexibility with your dates then book the best thing you can find - especially if the return is good. Then keep looking and at some point you should be able to find better outbound flights. When you do, call in and pay the $90 change fee.

I would also try to find outbound yow-yul-zrh (on LX) or yow-yyz/iad/ord-ist (on TK). I prefer going east on the outbound since I would rather leave in the evening and arrive in the morning. Also no YQ on LX or TK.