All-two-dimensional magnetic tunnel junctions promise atomically sharp interfaces, yet the role of interface-induced states in their spin transport is not fully understood. Here, we theoretically investigate spin-dependent transport in van der Waals magnetic tunnel junctions of the structure Cr₂C/MY₂/Cr₂C (M = Mo, W; Y = S, Se) with barrier thicknesses of 3, 5, 7, and 9 layers. The broad features of the k_∥-resolved conductances, namely suppression near the Γ point and enhancement at six off-Γ hot spots, are consistent with the decay of evanescent states in the barrier. However, trilayer WS₂, MoSe₂, and WSe₂ barriers exhibit conductances of the order of e²/h at k_∥ points within the hot spots. We attribute these near-unity transmission channels to resonant coupling between the interfacial states at the two electrode–barrier interfaces, as evidenced by their weak but finite residual weight at the barrier center. For thicker barriers, this coupling weakens, which suppresses the residual weight, thereby reducing the tunnel magnetoresistance (TMR) ratio of the MoS₂ junction while enhancing those of the other junctions. To exploit the interfacial states for spin-selective tunneling, we further examine biaxial tensile strain applied to the trilayer junctions. At 4% strain, the TMR ratio increases from 176% to 540% for MoS₂ and from 98% to 496% for WS₂, whereas MoSe₂ and WSe₂ exhibit comparatively weaker enhancement. Our results establish interfacial-state engineering via strain and barrier thickness as effective routes for enhancing the TMR effect in all-two-dimensional magnetic tunnel junctions.