Delta will take anybody on their reiprocal list, make sure you passport list at least 90 minutes prior to departure at the International Service counter, otherwise you won't get on the flight.
Also, if going on Delta, make sure to look up exactly how your company is listed in their system. Leaving the US usually isnt a problem, coming back can be. At the time I worked for Atlantic Coast Airlines, Delta Connection. I told the gate agent both, they couldn't find it. It was listed under ACA/Delta connection. They were nice and patient while they let me look through the list on their computer. I've heard some places are not as nice and if they can't find you, tough.
Coming back into the country, get to the airport atleast 2 hours early, and be prepared to pay a departure/extortion tax. As dorky as it is, it helps to wear your uniform, you gt alot more respect.
CAL and AA will only take you if your company is on their "International Reciprocal Jumpseat List". Even if you work for an Express/Connectin carrier that goes to Mexico/Canada, that doesn't count as being Int'l to them. I have heard though that if you can make it past the gate agent, a CAL guy will let you on, can't confirm it though.