I'll be going from Canada to Florida in October for top surgery.
My name won't be changed till November, and my legal sex not until well summer 2014.
6 month on t I pass flawlessly. The picture on my passport is of me pre-t.
Costs a lot for a new passport, especially if I'll be changing it again in 2014.

I'm extremely anxious about the airport. (Even though I've taken the plane around 60 times already.)
Legally, Canada does not permit someone to fly if they do not present as their legal gender.
Never heard about any agent though pushing that law but it's still extremely stressful.

Anyone have any experience with this? Or suggestions? Or anything?

Well, I've not dealt with Canada, but have flown internationally numerous times passing as a male (with beard, etc.) and having a pre-T photo and name on my passport with no issues (half the time, they don't look that well or question it as long as you somewhat resemble your photo - but to be safe, I always carry a letter from doctor stating that I am undergoing medical transition from a female to male somatotype and I also carry my change of name certificate from Australia).

What constitutes "presenting as your legal gender"?  Does that mean all "women" must wear dresses and a face full of makeup and all "men" must have huge bushy beards and wear flannel shirts?

I'd say not to worry about it as long as you somewhat resemble your passport photo.

If they say anything to you about presenting as male when your ID says female, just act offended.  Butch women dress male to the point of passing all the time. If they got stopped at airports for it there'd be stories about it. If you are that worried about it and you have facial hair, shave it and go with the same tactic.

A similar thread like this surfaced days ago. Like we said, you may present a letter from your doctor, psychologist, therapist etc...a written proof that X person is on the procedure of transitioning or bring your National ID card or any other identification driving lisence with a pic of your current face and if you don't have it's just a letter.

I travelled recently (not to Canada though) and I also look a lot different to my passport. My passport is some young girl with long hair wearing make up and I'm now a short haired dude who passes sometimes. I had no problems whatsoever, and I went through countries where they had the death penalty still, so I was bricking it. I also work in a shop and when I check ID I always look at the eyes mainly, it's a big give away. People's faces and hair change all the time, but their eyes stay the same. As long as your eyes are still the same, I can't imagine there being a problem. Like someone else said, if you have a beard, shave it and then go along your business. Good luck.

When I traveled for surgery TSA cared more about the bag of pee on my leg than how I looked or the M on my passport.  Canadian airport security shouldn't be too much different since they are looking more for prohibited items than go over everyone with a fine toothed comb who looks different from their years old driver's license or passport photo.

And yes, I got the special treatment for that, consisting of having my hands wiped with chemical detecting paper. And I hear ya on passport costs, not looking forward to the $120 or whatever to update mine.