Usually ATN. They will most likely fly you into LAX on Friday and then take Saturday afternoon flight to PPT. On the return, you will have a day room in PPT then the SAturday night flight to LAX then back home to Toronto on Sunday.
The other possibility is Air France. They will fly you to LAX on Friday and then the midnight flight to PPT. There, you will have a day room before boarding at 1500. On the return, it is an early Saturday am flight to LAX. I don't know if they make you take redeye back to Toronto or put you up overnight.
Most people prefer the first option as they don't want to take the overnight flight. We are paying the deviation to ensure the second option so we can get onboard earlier and also fly out earlier on Saturday (avoid hot evening in non airconditioned airport).