Ronaldo helped Real Madrid to a second consecutive Champions League title and finished as the tournament's top scorer with 12 goals.
Goalkeeper Buffon led Juventus to a sixth successive Serie A title, a third-straight Italian Cup success and a runner-up finish in the Champions League.
Messi claimed the Spanish King's Cup with Barcelona and finished as La Liga's top scorer with 37 goals last season.
Messi and Ronaldo have both won the award twice, with the Portugal international voted winner last year.
VfL Wolfsburg striker Pernille Harder, Olympique Lyon midfielder Dzsenifer Marozsan and Barcelona winger Lieke Martens were shortlisted for the UEFA's women's player of the year award.
Martens was named the Women's Euro 2017 player of the tournament earlier this month after helping Netherlands to their first senior female continental title.
The awards will be presented at this season's Champions League group stage draw in Monaco on Aug. 24.