UEFA also announced their list of nominees for the best goalkeeper, defender and midfielder from last season's tournament.
Messi scored 12 goals in the tournament as Barcelona reached the semifinals before suffering a comeback defeat to eventual winners Liverpool. Meanwhile, Ronaldo scored six goals -- including a hat trick against Atletico Madrid -- as Juventus made the quarterfinals, where they lost to Ajax.
The two players are joined by Sadio Mane in the Forward of the Season category, while the Senegal international's captain at Liverpool, Jordan Henderson, is up for the Midfielder of the Season award, alongside Tottenham's Christian Eriksen and Frenkie de Jong, who joined Barcelona from Ajax this summer.
De Jong's former Ajax teammate Matthijs de Ligt has been nominated for the Defender of the Season award, but faces competition from two more Liverpool players: Virgil van Dijk and Trent Alexander-Arnold.
Liverpool, who defeated Tottenham in last season's final, have one more player up for nomination in Alisson, who features in the Goalkeeper of the Season category, with Tottenham's Hugo Lloris and Marc-Andre ter Stegen of Barcelona also nominated.
The jury for the awards was made up of the coaches of the 32 clubs that competed in the group stage of last season's tournament, together with 55 journalists from each of UEFA's 55 member associations.
Both coaches and journalists selected a shortlist of three players in each category, but coaches were not allowed to vote for players from their own teams.
The awards will be presented in Monaco on Aug. 29 during the draw for the coming season's Champions League group stage.