Sunday's referendum, in which Moreno backs the "yes" vote, features seven questions including reintroducing term limits to prevent presidents from running indefinitely.
If the current head of state gets his way, Correa will not be able to join the 2021 election race.
According to initial polls, the "yes" camp -- supported by traditional opposition parties -- will win a comfortable majority with between 72 and 84 percent of the vote.
Upon entering office last May, Moreno -- Correo's deputy between 2007 and 2013 -- transformed into a staunch critic of his predecessor, whom he has called a proponent of "21st century socialism" and accused of leading a corrupt government.
Far from keeping Correa's presidential seat warm as expected, Moreno's calling of the referendum instead spells a clear invitation to enter a post-Correa era.
On top of question regarding indefinite re-election -- a law approved by Correa in 2015 -- Moreno proposes restructuring the body created by his former ally to select senior authority figures such as judges.
In practical terms, removing its current members would represent a total "de-Correazation" of the state.
"The margin (of victory) is what has to be looked at. If Lenin Moreno wins by a big margin, he will achieve the fundamental objective of the vote: legitimacy," political expert Simon Pachano told AFP.
Moreno, 64, only narrowly defeated conservative banker Guillermo Lasso in last April's election.
"All the 'no' votes will be Rafael Correa's. Suppose you have 40 percent, he can claim that and say we are the first political force in the country," Pachano added.
Correa, who ruled for a decade from 2007, has branded Moreno a "traitor" and the vote "unconstitutional", denouncing the president for wanting to achieve "absolute rule".
He also maintains that with a question over whether those convicted of corruption should be barred from politics, Moreno is trying to establish a legal barrier to Correa re-entering office.
"They will invent a crime against me to disable me. It is the right's new strategy to destroy progressive leaders," Correa, 54, previously told AFP.
Correa -- who returned to Ecuador from Belgium in January to embark on a solo "no" campaign -- is expected to testify in court Monday over alleged irregularities in million-dollar oil sales to China and Thailand made during his tenure.
His former vice president, Jorge Glas, was sacked by Moreno following his re-election and sentenced to six years in jail for corruption.