The effect of an external electric field on the bandgap is observed for two proposed heterostructures graphitic carbon nitride-graphene-hexagonal boron nitride (g-C₃N₄/G/h-BN) in hexagonal stack (AAA) and graphene-graphitic carbon nitride-hexagonal boron nitride (G/g-C₃N₄/h-BN) in Bernal stack (ABA). Their inter-layer distance, binding energy and effective mass has also been calculated. The structure optimization has been done by density functional theory (DFT) with van der Waals corrections. The inter-layer distance, bandgap, binding energy and effective mass has been listed for these heterostructures and compared with that of bilayer graphene (BLG), graphene-hexagonal boron nitride (G/h-BN) hetero-bilayer, graphene-graphitic carbon nitride (G/g-C₃N₄) hetero-bilayer and graphitic carbon nitride-graphene- graphitic carbon nitride (g-C₃N₄/G/g-C₃N₄) heterostructure in Bernal and hexagonal stack. g-C₃N₄/G/h-BN is found to offer lower effective mass and larger bandgap opening among the considered heterostructures.