In this work, we investigate electron energy spectra and localization in a three-dimensional harmonium system using the shifted 1/N-expansion method. Our results show that increasing confinement strength \(\upomega \) raises energy levels and reduces equilibrium interelectron distances, as stronger confinement forces electrons into tighter spatial regions. In the strong-correlation limit \(\upomega \rightarrow 0\) , we confirm the formation of a Wigner molecule. Additionally, we establish the transition from the Wigner molecule regime to a strongly confined state where quantum confinement suppresses correlation effects. Our results further show that energy levels increase by increasing the principal quantum number (n), while centrifugal effects lead to a slight reduction in energy levels with increasing angular momentum number ( \(\ell )\) . These results enhance our understanding of electron correlation effects in confined quantum systems and have potential applications in nanophysics and quantum computing.