On Saturday, Yushchenko said voters faced a choice between Ukraine's future and a dubious past.
"Either you vote for changes in your lives or you vote to bring back the past and those who have divided us and infected the very body of our nation," he told television viewers.
However, polls predict Yushenko's Our Ukraine-People's Self-Defence party will finish third in the vote behind Yanukovych's Party of Regions, expected to receive the most votes, and Bloc Yulia Tymoshenko in second place.
Yushennko defeated Yanukovych in a rerun of the presidential election in 2004 after the original result was declared invalid following a series of mass pro-democracy protests that became known as the "Orange Revolution".
Since then however, Yushenko has failed to implement many of the reforms he promised and Yanukovych, who favours closer ties with Russia, has undergone a political resurrection.
After being accused of rigging the presidential vote in 2004, he became prime minister after his party won a majority in elections in 2006.
Yushchenko is pinning his hopes on a last-minute alliance with Tymoshenko - a partnership that could give their parties control of parliament, even if Yanukovych's bloc wins the most votes on Sunday.
Forging a government coalition with Tymoshenko, however, could mean weeks of negotiation between their two parties, and Yanukovych has signalled that he would not give up power easily - threatening protracted election uncertainty.
Yanukovych, who draws his support from Ukraine's Russian-speaking east and south, fiercely resisted Yushchenko's decision to dissolve parliament in April and call new elections after the president accused him of seeking to seize power.
Yanukovych eventually agreed to the vote on Sunday, but has suggested victory would be the only outcome he is prepared to accept.
Voting begins at 7am (0400GMT) on Sunday, and polls close at 10pm (1900GMT), with exit polls available immediately. Official results are expected on Monday morning.
Ukraine has 37.5 million registered voters but irregularities in voter registration has increased fears there could be legal challenges to any vote.
Speaking to election monitors in the east of the country, Al Jazeera’s Lawrence Lee said he has heard reports of Ukrainian-Canadian monitors being harassed as they inspected voting facilities and irregularities in the number of people registered in some areas.
Lee said that 94,000 people were allegedly registered twice in the industrial town of Kharkiv in the east, while in the capital Kiev 15,000 double entries were reported.
Lee also said that an estimated 3,600 dead people were registered to vote and that one worrying report indicated that Russian names when translated into Ukranian by the voting machines would appear differently to how they do in passports.
This could endanger the ability of about 330,000 voters in Ukraine to cast their ballots.
Meanwhile in Kiev, Al Jazeera's Jonah Hull said that recent accusations against one another by the three leading parties seemed to indicate they were preparing for legal challenges and demonstrations once voting ends.
"It feels although these parties are preparing a pretext to be able to challenge the results of this election if they don’t like the way these results don’t fall down," Hull said.