Hosts Portugal booked a return to Estadio do Dragao, where they beat Switzerland 3-1 on Wednesday, thanks to a stunning Ronaldo hat-trick – the 53rd treble of his professional career.
Van Dijk brought an element of calm to the Dutch's error-strewn semi-final against England, which also ended 3-1 after extra time.
De Ligt erred to give away the penalty from which England took the lead but he responded by powering home a second-half equaliser.
The Ajax youngster enjoyed success against Ronaldo's Juventus in the Champions League this year and, with plenty of focus on the heavyweight tussle between Van Dijk and the five-time Ballon d'Or winner, Koeman was keen to point out both his centre-backs are fully equipped for the challenge.
"We played a friendly in Switzerland, not a long time ago, and De Ligt was stopping Ronaldo as well," Koeman told a pre-match news conference, reflecting upon a 3-0 win in Geneva last year when Van Dijk completed the scoring.
"It's not only Van Dijk who can stop Ronaldo.
"But Ronaldo is good enough to create against really good defenders. That's the nicest part of football - you can't do anything because his quality is on such a high level."
Perhaps unlike his colleagues further back in the line-up, Netherlands midfielder Georginio Wijnaldum has the luxury of looking forward to pitting his wits against one of the greats of the game.
"I'm happy that we play against him," the Liverpool midfielder said. "You always want to play against the best players in the world. It will be a big test for us to stop him.
"We all look forward to playing a game against Ronaldo, but it's not only him. He has a big influence on the team, and it's difficult to stop it.
"They have more players who can make the difference, as a team we have to do well to stop them."
Daley Blind, who played at centre-back alongside De Ligt at Ajax this season and operated at left-back outside Van Dijk in Guimaraes in midweek, believes the whole team has a defensive job to put in against a gifted Portugal side.
"They're both great defenders. I think it's comfortable next to them," he said.
"Matthijs is a big talent, Virgil is showing his qualities all season long.
"But our defence starts with our attacks – you can see on the two goals we scored against England [in extra time] when we won the ball high up the pitch and to create chances."
Netherlands have undergone a rapid resurgence since Koeman's appointment last February, having failed to qualify for either Euro 2016 or the 2018 World Cup.
"We know in Holland we can play football but maybe the difference now is there is more focus, more togetherness, more energy in the team," Koeman added. "This is what I think has made the improvement of this team."