Contradiction with Matthew 27:32
This verse contradicts Luke 23:26 by stating that Simon of Cyrene was compelled to bear the cross, whereas Luke implies a voluntary action.
Matthew 27:32: And as they came out, they found a man of Cyrene, Simon by name: him they compelled to bear his cross.
Contradiction with John 19:17
This verse contradicts Luke 23:26 by specifying that Jesus bore his own cross, whereas Luke mentions Simon of Cyrene carrying the cross for Jesus.
John 19:17: And he bearing his cross went forth into a place called [the place] of a skull, which is called in the Hebrew Golgotha: