This study focuses on the microarchitecture-dependent nonlinear bending behavior of cellular plates with equitriangularly prismatic microarchitectures by adopting a dimensionally and constitutively reduced strain gradient plate model. The strain energy formulation is based on the dimension reduction of the first-order shear deformation plate theory along with von Kármán's nonlinear strain relations and anisotropic strain gradient theory. The classical and higher-order constitutive parameters are obtained according to the recently published homogenization results for a corresponding linear plate model. The corresponding finite element simulations, numerically solving the anisotropic strain gradient plate problems, rely on a nonstandard, higher-order, six-node triangular element showing good convergence properties. Comparisons between the proposed (2D) strain gradient shear deformation plate model and the corresponding (3D) detailed full-field reference models demonstrate for a variety of cellular plate structures that the accuracy of the proposed approach is at a very good level with relatively low computational costs. A diverse set of numerical examples is provided in order to investigate the size-dependent nonlinear structural response of cellular plates having different numbers of microarchitectural layers, midsurface shapes and boundary conditions.