The Twenty20 final in Lahore will be the first time a Sri Lanka squad has played in Pakistan since gunmen staged a deadly assault on their team bus in March 2009.
Sri Lanka Cricket is pushing ahead with its tour despite ongoing concerns about security and top players being left out of the squad for the three-match series.
The board has played down speculation in local media that coach Nic Pothas and team physiotherapist Nirmalan Dhanabalasingham will also not travel to Pakistan.
"We are going to be in Pakistan for just over a day, but it is very important for us to go there and revive international cricket in South Asia."
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No top international side has played in Pakistan since the 2009 attack, which left eight people dead and seven visiting team members and support staff injured.
Sumathipala, who will join the squad for the match, said the board had accepted security assessments conducted by Sri Lankan and Pakistani authorities.
Several players who had said they would not travel to Pakistan have been dropped from the series, which opens in the United Arab Emirates on Thursday and concludes with the final in Lahore.
On Saturday, Sri Lanka made 28-year-old allrounder Thisara Perera the captain of the T20 squad.
He had toured Pakistan as a member of a World XI for a three-match Twenty20 international series played in Lahore last month.
The World XI series was part of Pakistani efforts to bring international cricket back to the country.
Pakistan hosted Zimbabwe for a five-match limited overs series in 2015 but top teams have refused to tour there, forcing Pakistan to play home matches in neutral venues in the UAE.
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