Buffon has won numerous trophies throughout his illustrious career, but Champions League glory has evaded the veteran shot stopper until now.
The 39-year-old lost the final in 2003 and 2015 and he will be hoping it is third time lucky in Cardiff this weekend.
"Had the opponent not been Real Madrid, I would have wanted Buffon to win the Champions League with all my heart, he deserves it," Casillas told La Gazzetta dello Sport.
"I obviously support Madrid, but Buffon's career should not come to an end without him having won the Champions League. He has won almost everything, except this one and it is weighing down on him.
"He has had a great season and that he is in the final again is something positive for the old players like Petr Cech and me. He is showing that you can still do well and be competitive at the age of 39.
"Maybe he can win the Ballon d'Or, but that is something very complicated for a goalkeeper.
"The final will be a very even game. Juventus have always been strong in defence, but they are now also strong in attack. I would say it is a fifty-fifty game."