My son was born in the us 1979 at an early age I had to send him to my parents so I can work, he is grown now, I use to get an allowance for him monthly but since he was not in the us , I stopped getting it does he have retro money's waiting to be collected. I have his social security card.
If by 'allowance' you're referring to Social Security child's benefits, then most likely your son's benefits would have been sent to your parents while he was living with them. Social Security appoints a representative payee to handle benefits on behalf of minor children, and the person with custody of the child generally acts as their payee.
U.S. Social Security benefits can still be paid to people living in Canada, so your son's benefits wouldn't have been suspended simply because he was residing outside the U.S. Therefore, assuming that your son's benefits were paid to someone else while he wasn't in your care then there are likely no unpaid benefits waiting for him.