Your question depends on whether he still has a valid green card. If he does, you would use his SSN number. If he does not, most likely you would use whichever form the insurance company requires. It will probably be W8BEN.
The other form is mostly for payment of life insurance death benefit to a foreign person.
Since you are applying at NYL, you would fill out whatever they require. W8 Ben should be sufficient. SSN numbers don't expire so you would use that number on the W8Ben.
In the old days, NYL used to issue permanent only contracts with no riders to Canadian Citizens. I don't know if that has changed. Don't expect them to offer wp or SPPO riders to foreign citizens.