I am an AC Elite, branching out to another program/carrier.
I will be flying YVR-CUN-SEA in BF on CO in January.
I am not member of any of the aforementioned FFPs.
I do some Westcoast and OGG flying ex YVR. As of now I primarily use AC. I would be open to using another carrier. I have flown AS in F before and was impressed by the friendliness of the cabin crew.
Which of the aforementioned FFPs should I enrol in, so that I can earn points/miles for my upcoming flights?
I understand that I can enrol in a ny one of these programs, and that miles from all three carriers can be accrued to the same account, is this correct?

Thanks is advance for your opinions and ideas.