The march was organized as a show of solidarity with minorities across Belgium and as a way to ease ethnic tensions in the port city of Antwerp, said Mayor Patrick Janssens.
Organizers said they expected 50,000 people to participate. But police said they expected fewer to show up due to the rainy weather.
The silent procession, in which participants were asked to wear white and businesses requested to put out white flags in solidarity, will wind its way through the streets of the historic city center, near where the two victims were gunned down in broad daylight May 11.
The 18-year-old man who is accused of the crimes also shot and seriously injured a woman of Turkish origin before police shot him in the stomach. The suspect, who has been charged with murder, remains under guard in hospital.
The murders, which police believe are racially motivated, happened in a city which has for years struggled to keep peace between ethnic communities.
Antwerp is the home of the popular anti-immigrant Flemish Interest party, and large Orthodox Jewish and Moroccan communities.
While the Flemish Interest leaders quickly condemned the killings, the victims' families urged them not to use the murders to drum up support for their far-right political platform, or to participate in the march.
The party, previously known as the Flemish Bloc, won about one third of the vote in Antwerp in 2004 regional elections and looks set to gain even more seats in this year's municipal elections, the AP reports.
The family of the two-year-old toddler, Luna Drowart, who was buried last week, has declined to participate in the march, while relatives of the slain baby sitter, Oulemata Niangadou, 24, who was repatriated to her home country of Mali were expected to attend.