All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is permissible for the suitor to look at the girl to whom he is proposing for a need, and it is impermissible without a need. If the suitor looked at the girl and decided that he liked her or not before cancelling the engagement, it is impermissible for him to look at her again because she is a non-Mahram (marriageable) to him.
Shaykh Ibn ‘Uthaymeen was asked, "Is it permissible for a man to propose to a woman and that she remains engaged to him for more than two or three years and he continues to look at her?" He replied, "Looking at the woman one is proposing to is allowed for a need only. If he looks at her the first time and he liked her or did not like her, then he should act upon this, and there is no need to look at her again, because he has already decided whether he would carry on with the engagement or not. It is impermissible for him to continue to look at her for no need because she is a non-Mahram woman." [Fatawa Noor ‘ala Ad-Darb]
However, if the suitor fears that her appearance might have changed, which would cause him to change his mind about the marriage, then he may look at her again because the rationale behind the permissibility of looking at her the first time recurred, namely the need to look at her in order to decide whether to carry on with the marriage or not.
Allah knows best.