Robertson Davies' Fifth Business is neither about despair nor hope but about the necessity of suffering in life, particularly in reference to spiritual life. A core Buddhist axiom states that "Life is suffering," and nowhere is that more clear than in the lives of the saints, a topic with which protagonist Dunstan is obsessed.
Given the context of the question, it's important to parse out why suffering is not the same as despair. Suffering in the sense of martyrdom is considered a blessing, specifically in Catholicism. Some people are burdened with great suffering—for example, a cruel death or particularly challenging life—in order to help them grow closer to God. The Vatican, in the Catechism of the Catholic Church states, "Suffering, a consequence of original sin, acquires a new meaning; it becomes a participation in the saving work of Jesus" (Pt. II, Ch. 2. "The Sacraments," IV 1521). Throughout the novel, Dunstan suspects that Mary is actually a saint because of her suffering, and he even grows jealous of (what he suspects to be) strong faith. In this context, suffering is closer to hope than despair.
Because Fifth Business incorporates postmodernist, mythological, and surrealist themes, it's fair to say that hope and despair are in the eyes of the beholder. Life, and the novel, is both at once.