the other two Tan are only for show.
this TT will surely win
If the election period extents over 9 days, with each candidate allowed to hold election speeches at each of the stadiums on the government's expense (they can appear jointly), then the chances are equal for each of them
However since the candidates are allowed only 1 election rally, Dr Tony Tan has the advantage. This is because he had constant exposure to the public in the past, the public know his track record and he speaks well (compared to the video of TKL speaking).
Because of Dr Tony Tan's track record, the televised profiles will show the other two poorly, relatively speaking.
As a result, Dr Tony Tan is likely to win.
Again, it depends on how much the public believe that Dr Tony Tan is independent of the PAP, despite his resignation. And how much they value this quality of 'independence' in the President.
There is still a chance for the other two.
Besides the vote is never final until it is counted.