Why will CuSO4 solution be acidic?
Because the second pKa of sulfuric acid is weak, sulfate withdraws protons from water.  Therefore, the contribution of sulfate alone is to make the solution slightly more basic than pH 7.

However, as quantified in CE4501 Environmental Engineering Chemical Processes, Cu will form species such as CuOH+, which is the reason the solution will be acidic overall.  This could be approximated by thinking of $\ce{Cu(H2O)6^{2+}}$ as having a pKa of ~6.3.  

Because  $\ce{HSO4-}$ is a stronger acid than CuOH+ is a base, the solution is acidic.