The Real Madrid forward will become only the third Portuguese player to collect 100 caps, after Luis Figo (127) and Fernando Couto (110).
But he will be the first to reach that milestone before the age of 30.
The 27-year-old Ronaldo made his debut in 2003 when he was 18. He has scored 37 international goals, a mark bettered only by Pauleta (47) and Eusebio (41).
The Portuguese need a win over Northern Ireland in Porto to get their 2014 World Cup campaign back on track after a 1-0 loss in Russia last week.