The evidence is 1 Cor 15:3-8:
For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, 4 and that He was buried, and that He rose again the third day according to the Scriptures, ...
"First of all'' means that that was the first teaching by Paul given to the Corinthians hence they didn't need to know who was the Lord Jesus: they knew already him.
Hence the only possible logical conclusion is that there was a pre-Christian cult of a not-crucified Joshua in Corinth.
The news from Paul and the Pillars before him were only about the crucifixion of this already known Joshua.