There seems to be two popular candidates at the moment, Yavas(Mayor of Ankara) and Imamoglu. Imamoglu looks to be more ambitious, thus it is likely he will run

There seems to be two popular candidates at the moment, Yavas(Mayor of Ankara) and Imamoglu. Imamoglu looks to be more ambitious, thus it is likely he will run for presidency. All the current polls suggest either of them could win against Erdogan if the opposition can form an united front. It is easier than it would be in a parliamentary system, since if no candidate secures over fifty percent of the votes in the first round, the top two candidates go for the second round of elections. And yes, the opposition parties declared the next government would be a transitional one and curb the powers of the president Erdogan has formed some paramilitary organizations in the recent years and these are worrying. However, the opposition literally watches over every single vote with multiple volunteers, lawyers and every single vote table gets recorded online in real time. It would be certainly hard to pull of a blatant fraud. Thats how opposition managed to win major cities few years back, against all corrupt judiciary branch.