Some routes to KEF are seasonal. I have read that OS flies there from VIE at certain times of the year. This would certainly be one of the most "direct" routes to get there from YYZ. Not sure if YQ applies to OS as I haven't looked.

I'd suggest you look at flying SK from IAD to CPH. You might be able to create YYZ-IAD-CPH-KEF as a valid route. Another alternative would be to just purchase a fare on FI once you're in Europe. Many FI fares are surprisingly affordable.