"What is at stake are two visions of society, two visions of development, two visions of the state," said Correa, 53, a leftist economist who oversaw an economic boom in the oil-rich country of 16 million over his decade in power.
He is not up for re-election, and voters must decide whether to continue his Socialist agenda by electing Lenin Moreno, or to follow Argentina, Brazil and Peru in switching to a conservative government.
Moreno, a Correa ally who leads in opinion polls, promises to continue the outgoing leader's tax-and-spend social policies.
Boom, bust
"The Ecuadoran people have affection (for us) and are determined to continue with this process," the 63-year-old told AFP on Wednesday at a campaign event.
But in an uncertain contest, Moreno faces a challenge from conservative ex-banker Guillermo Lasso, 61, second in the opinion polls.
He has vowed to cut spending and taxes, lure foreign investment and create a million jobs, while also slamming Correa's allies over alleged links to a corruption scandal.
"We have to vote for change to fight against corruption," Lasso said at a campaign rally on Wednesday.
The third-placed candidate is conservative former lawmaker Cynthia Viteri, 51.
Ecuador's economy shrank by 1.7 percent last year, suffering notably from falling oil prices.
Correa is accused of failing to save any petrodollars for a rainy day, and of hampering business with high taxes and duties.
"When Correa came to power he promised to diversify the production model," Alberto Acosta-Burneo, an economist at the Spurrier Group consultancy, told AFP.
"But he is leaving behind a country in which it is very difficult to produce things."
Impact on Assange?
Opinion polls indicate Moreno will likely win Sunday's first-round vote.
But if his lead is not big enough, he will face a runoff on April 2 against a conservative rival, most likely Lasso.
Polls show a high ratio of undecided voters.
"Any party could beat the governing one in the second round, because there is major resistance to and rejection of the government," said political scientist Paolo Moncagatta of Quito's San Francisco University.
But Michael Shifter of the Inter-American Dialogue think tank in Washington cautioned: "It is a mistake to underestimate the strength of support for Correa's side."
Voters will also elect a new parliament.
Polling stations will open from 1200 GMT to 2200 GMT. Results are expected from about 0100 GMT Monday.
Another issue that hinges on the outcome of the election is the fate of fugitive WikiLeaks founder Julian Assange, who has been living in the country's London embassy for nearly five years.
Moreno favors continuing to grant the Australian whistleblower asylum, given to him under Correa.
But Lasso and Viteri both told AFP they would end Assange's asylum if they win.
Under Correa, Ecuador grabbed world headlines when it defied the United States by granting Assange refuge as he fights against Swedish rape allegations.
The move has also shielded him from arrest over possible extradition to the United States for leaking diplomatic cables.
WikiLeaks has said Assange could travel to the United States to face investigation if his rights were "guaranteed".
Correa says Latin America needs a strong leftist movement to resist US President Donald Trump's hard line on immigration and trade.
But both Lasso and Viteri have shown more willingness to work with Washington since Trump's election victory in November.
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