Portugal won the tournament in 2016 and begin their title defence on Tuesday against Hungary, in Budapest, in their Group F opener.
"I feel as motivated or even more than in 2004 when I played my first European tournament," Ronaldo told Canal 11.
"We are the defending champions, and we are part of a new group of candidates to win the trophy."
Portugal have one of the most talented teams in the tournament with the likes of Ronaldo, Manchester United's Bruno Fernandes and Manchester City's Ruben Dias, who was voted as the Premier League's best player of the season, among their ranks.
"The Portuguese can expect the same as always, a national team with a lot of enthusiasm and ambition," Ronaldo said.
"We have a positive thought which is that things are going to go well. I asked the Portuguese people at home and abroad to think positively."
The Juventus forward, who will feature in his fifth European Championship, said his team are ready.
"We have worked well, my teammates and I, as well as the coach," the 36-year-old added.
"The groundwork is done and we just need to finetune a few things.
"Now is the time for the ball to roll so that Portugal can give its best and start the tournament on the right foot with a win against Hungary."
"These are the opponents we have and we are going to play against them," he said. "There are no easy games.
"There is no point and it serves for nothing to promise titles or make predictions. What I hope and desire is that things go in the best possible way."
Ronaldo goes into the tournament looking to break a few records. Should he score in this tournament, he will become the leading scorer in men's Euro finals as he is currently level on nine goals with France great Michel Platini.
Ronaldo has also scored 104 goals in 175 appearances for Portugal, just five fewer than Iranian Ali Daei's all-time men's record of 109 international goals.