On the eve of the vote in the lower house of Congress, the 68-year-old leftist leader published a searing column reaffirming her belief that she was the victim of a "coup."
"They want to convict an innocent woman and save the corrupt," Rousseff wrote in the daily Folha de Sao Paulo.
The political crisis is threatening to destabilize Latin America's biggest economy as it struggles through a crippling recession and prepares to host the Rio Olympics in four months.
"She will stay (at her official residence) for the last negotiations for Sunday's vote," a presidential advisor told AFP.
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Organizers hope that more than 100,000 will gather at the rally and the support camp this weekend.
"We came to join the defense of democracy and the government that was legitimately elected in 2014," said Tiago Almeida, 35, a metal worker from the state of Sao Paulo who has been at the camp for days.
Police tightly guarded the area around Congress, which was surrounded with metal barriers.
Pro- and anti-Rousseff rallies are also planned in other cities on Sunday, including the economic capital Sao Paulo and Rio de Janeiro, where the Summer Olympics will be held in August.
Lower house lawmakers debated the impeachment on Saturday and were due to vote late Sunday on whether to call for an impeachment trial.
Rousseff faces charges that she illegally used creative accounting to mask government shortfalls during her 2014 reelection.
She accepts the accusations but defends her behavior by saying that previous governments used similar measures.
Cardozo said the government was considering further legal appeals.
"This is a historic process, there's no doubt," said House Speaker Eduardo Cunha, one of the leaders of the push to remove Rousseff.