* Guinea Bissau seeks to turn page on years of instability
* Former finance minister seen as most likely winner
* Fears of post-election violence linger on
By Alberto Dabo
BISSAU, May 17 (Reuters) - The frontrunner in Guinea-Bissau's election ended his campaign by calling for peace as the coup-prone West African country prepared for a Sunday vote meant bring political stability and renew cooperation with donors and investors.
Former finance minister Jose Mario Vaz, candidate of the dominant party African Party for the Independence of Guinea and Cape Verde (PAIGC), secured more than 40 percent of the vote in the first round.
In the runoff he faces Nuno Gomes Nabiam, an independent candidate backed by the army and the country's balanta electorate. Nabiam won 25.14 percent of the first round vote.
The election is meant to offer the nation a fresh start after decades of instability since independence from Portugal in 1974. Its last vote in 2012 was abandoned after the military seized power between rounds of voting.
"I am asking the army not to get mixed up in political matters and to remain in barracks," Vaz said late on Friday before a crowd of around 20,000 supporters in National Heroes' Square. "I am also asking the people to forgive each other and for nobody to spread terror in our country."
Weak state institutions, along with its array of islands and unpoliced mangrove creeks, have made the country a paradise for smugglers of Latin American cocaine destined for Europe.
No elected leader has completed a five-year term in Guinea-Bissau and analysts say donors and regional powers who have been bankrolling the interim administration are frustrated with the recurrent crises.
In his final speech ahead of the poll, Vaz said that he would fight to reduce poverty and pledged more investment in agriculture. Nabiam said he would seek to form a united government focused on health, education and tackling youth unemployment.
"It's the beginning of a new era that needs to be marked by radical change," Nabiam told supporters.
The final two weeks of campaigning in the country have mostly taken place in a celebratory atmosphere.
On Friday, long convoys of vehicles with the two candidates drove up and down the two main avenues of the capital Bissau honking their horns ahead of the final speeches.
Both candidates have officially said they will accept the results regardless of who wins. But Dr. Marie Gibert, an expert on Guinea-Bissau at Nottingham Trent University, said it was "not impossible" for jilted supporters of the losing candidate to attempt a coup.
"Much will depend on the reaction of their support bases. This is particularly true of the army if Vaz is declared the winner," she told Reuters on Saturday.
Aly Diallo, a 32-year-old mechanic, said he was concerned about violence after the results are announced.
"I'm worried because Jose Mario Vaz doesn't have a great rapport with the soldiers and that was the case with Carlos Gomes Junior," he said, referring to the PAIGC candidate who was tipped to win the last presidential election before an army intervention.
Police sources said that around 5,000 men made up of police and forces drawn from the Economic Community of West African States had been deployed since Friday to provide security until the results are announced.
They said the army had been forbidden from mobilising on the day of the vote.
Jose Ramos-Horta, U.N. Special Representative in Guinea-Bissau, said he was "cautiously optimistic" about the result.
"There is awareness in the country, even amongst the soldiers, that things must change in the country," he told reporters last week. (Writing by Emma Farge; Editing by David Gregorio)