Hundreds of people are expected to walk through the County Tyrone town in what is being called a march for peace.
The Catholic constable, 25, died when a booby-trap car bomb exploded outside his home in Omagh last Saturday.
Police have said another bomb - found in a van near Newry on Thursday night - may have been intended for a high-profile town centre attack.
That would have been reminiscent of the devastating blast which wrecked the centre of Omagh in 1998, killing 29 people including a woman who was pregnant with twins.Widely condemned
Organisers of Sunday's rally say they intend to send a message to those who want take to Northern Ireland back to the violent past.
Recent bombings and attempted attacks have been widely condemned in Northern Ireland.
But the Newry discovery has reinforced police claims that the condemnations have had no effect on the dissidents responsible.
And police believe officers such as Constable Kerr are still being targeted.
PSNI Ch Supt Alasdair Robinson said the Newry device was "sophisticated and substantial", and could have caused huge devastation and loss of life.Police activity
The 500lb bomb was stored inside a wheelie bin in a van under the main Belfast to Dublin road.
Police believe the van containing the bomb was abandoned in the underpass because of increased police activity following the murder of Constable Kerr.
Army bomb experts carried out several controlled explosions on the vehicle on Friday night.
The van was stolen in Maynooth in the Irish Republic in January but police have refused to be drawn on which organisation was responsible.
The alert began shortly before 2300 BST on Thursday and the road did not reopen until Saturday.
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