It doesn't look like either Finns or (remaining unspecified number of) Karelians would want that.

I also have to point out that Karjalan istmus some Finns consider their Karelia is not in Karjalan Tasavalta mentioned in the article.

Nah, we in Finland tend to disagree.

My grandfather was evacuated from Karelia because Soviet Union occupied his hown town. And he would have deserved to get back to his childhood sceneries.

But now he's dead, of old age.
When I visited Karelia, I saw how everything was destroyed. It is one of the poorer parts of the Russia. Everything is incredibly derelict and rotten. You can kind of see some Finnish roots here and there in the architecture, but all in all, it's no longer reasonably salvageable. It would drain mad amounts of money to get Karelia into a condition suitable as human habitat. Countries have had different borders during the centuries. There's a certain time after which a change of borders is a fait accompli. I'd say that time is when the people who were at least 5-year-old during the beginning of the occupation have died of old age. So, some 80-ish years.

Also, we wouldn't be able to get Karelia back without its inhabitants. Because of the status of Swedish language in Finland (6 % speak it, and it's official an equal language with Finnish over here!) it would be almost impossible to not have tri-lingual street signs in Helsinki if we got all those Russians. The first parliamentary elections after the new territories would have joined would look completely alien to what we are used to.

It used to be the heart of Finland's industry. Viipuri used to be the cultural capital of Finland, more important for Finns of 1930's than L'viv is to Ukrainians of 2025. But the industry has been destroyed decades ago by mismanagement and the vibrant culture of Viipuri is dead for good.

I don't think much more than maybe 2 percent or so of Finns would want that land back. Maybe, if we only got some forests and fields and wouldn't need to think about what the hell to do with all those derelict villages? But otherwise: A strong no!