Also scheduled to speak are former Chargers coach Bobby Ross and former NFL safety John Lynch.
Seau committed suicide on May 2 at his home in suburban Oceanside. He played 20 seasons in the NFL, the first 13 with the Chargers.
Harrison and Tomlinson were teammates of Seau's with the Chargers while Ross coached Seau from 1992-96.
The master of ceremonies will be Miles McPherson, a former Chargers safety who's now the senior pastor at the Rock Church in San Diego.
Seau's funeral will be private.