I'd say try KLM but you'll probably get redirected to a local carrier
that flys to Amsterdam anyway, and will cost the appropiate amount from where ever your flying from.
Amsterdam is THE european hub, so you may get some deals from obscure airlines that use it, entirley depends on your location, Toronto is gonna be expensive unless you know someone in the industry.
Im local so $160 rtn any old airline max, but I'm the sort that will live in an airport for a week to get a good cancellation.[anywhere]
Amsterdam is one of the best capital cities Ive visited in the world,
tho hotels can get full in conferance season, as anywhere, so beware.
You will have a good time ,you just won't remember any of it