Tidus is just a dream of the Faith, "built" thanks to the memory of a real citizen of the real Zanarkand, Shuyin. The coincidence are enough, IMMO, to say that the Faith wants to use a old memory to give the same will and feelings of the original one.

It is true, at the first time Tidus is not in love with Yuna like Shuyin was for Lenne, but he's the man who can change the drastic situation of Spira, and saving the summoner too.

Despite that, the two of them are pretty different: looks like Shuyin is more hot bloodeed, he wants to destroy all Spira if it's usefull for save Lenne, Tidus is happier , he has suffer enough for Jech and her mother and he wants to come back to Zanarkand, so he tends to be gentle and more introspective.