I live close to the border on the states side and I'm also interested in decent rates out of Seattle. I did ok last year on a non-stop on Alaska Air, but I'm hoping to cut those costs even more. I booked 6 months in advance last time. We were going in June so I'm sure that played into it, this year we're going in September. When are you going?
I've had trouble with Delta out of SEA. They tend to cancel a lot of flights if you book early and change flight times out of the blue. Continental's service to Florida seems to be ok (other than a late start last time). Frontier won't get you there (unless they've changed), neither will JetBlue (Ok, JetBlue will get you there, but won't get you home). Southwest doesn't seem to run any specials for us out of SEA either.