Help my father get to my wedding

I am writing this on behalf of my father, who currently resides and works in Korea. He was a landed immigrant in Canada in 1997, and soon became a permanent resident a year after that. Then he chose to return to Korea to continue his work, travelling between Canada and Korea half a year each, in an effort to meet the requirement of the residency.

Eventually, he wasn't able to keep up with all the travel requirement and had to make a decision in 2007. He decided to give up his residency and stay in korea to continue his work. He assumed by not meeting the required length of stay in Canada that his permanent residency was automatically forfeit and destroyed his PR card.

Now with the change in travel document requirement, he cannot apply for eTA since he has been a permanent resident in the past and probably still lingers to be in the files somewhere, and he cannot file to give up the permanent residency because he cannot remember the original PR number, as it is a required section in the document.

He wishes to proceed with giving up current PR status, so he can obtain eTA for travel as soon as possible to come for my wedding, which happens in a few months.

Is there anything he can do to pull him out of this limbo?

And if he files to give up his PR status now, will he be able to apply for one again in the future?