According to Catholicism, how does God expect us to realize the truth of Christianity? I am sincerely sorry if this is under-researched/sourced, but according to Catholicism, how does He want people to discern [Catholic] Christianity's veracity? I have posted this on other SE religion sites.
God "expect[s] us to realize the truth of Christianity" through the Church that He founded, which is guided by the Spirit of Truth, the Holy Ghost.(cf. Cdl. Manning's Temporal Mission of the Holy Ghost)

The reason Christ founded the Catholic Church is summarized in the Great Commission he gave to the Apostles (Mt. 28:19):


  Going therefore teach ye all nations: Baptizing them in the name of the Father and of the Son and of the Holy Ghost.


The Catholic Church, "the pillar and ground of truth" (1 Tim. 3:15), exists to baptize and teach the truths necessary for salvation. 

Pope Pius XII wrote in his encyclical Mystici Corporis Christi §22, showing what makes one members of Christ's Mystical Body, His Holy Church:


  only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed.


To be a member of the Church, one must be baptized and profess the true (Catholic) faith.

How does one "profess the true faith"? He must submit to the teaching authority (Magisterium) of the Church and allow Her to teach him the truths necessary for salvation.