If he got a PR card in 2003 and has lived outside Canada ever since, he does not meet the PR residency requirements which would be a problem.
If he is visa exempt, he could still come and visit you on his passport. If they let him in without revoking his PR status, he would have to stay for 2 years and you could then apply to renew his PR card.
If he is not visa exempt, you could apply for a travel document for him to return to Canada at the Canadian embassy where he lives. They may refuse based on him having lost his PR years ago but they may also approve based on him having been a very young child and not able to control where he lives. If he gets the travel document, he could return to Canada and live with you and renew his PR card.
If the above don't work out, you can sponsor him again. A PR is allowed to be outside Canada for up to 3 years in a 5 year period. That also goes for children so if he is not going to be staying in Canada for at least 2 out of 5 years after you sponsor him, you are wasting your time because he will just lose it again. You can also wait to sponsor him again until he is ready. You can sponsor him at any time while he is under 22 and not yet married or in a common law relationship.