Smart cables extend submarine communication infrastructure toward marine environmental sensing and sensing-data backhaul. This paper investigates a multi-core fiber (MCF)-based prototype in which high-speed communication traffic and discrete-sensor data are routed through different spatial cores rather than sharing the same optical core. A 100 km weakly coupled four-core MCF was characterized and used as the central spatial-routing section, with two cores assigned to bidirectional communication and two cores to bidirectional sensing-data backhaul. At 1625 nm, the measured inter-core crosstalk (IC-XT) values for the four reported measurements were $-53.1$, $-52.6$, $-51.2$, and $-53.7$ dB/100 km. The same MCF section was incorporated into repeatered and unrepeatered hybrid laboratory configurations, with additional single-mode-fiber spans extending the total link lengths to 500 km and 300 km, respectively. Under the tested 400 Gbps condition, no frame loss or system alarm was observed during 17 h of operation; the round-trip delay was approximately 2.35 ms and the packet jitter remained below $0.3\mathsf{\mu }\mathrm{s}$. The sensing-node velocity channels recorded transient vibration responses and long-duration spectral distributions consistent with those of a reference CDS-E20 seismometer. These results support the feasibility of spatial-core routing for MCF-based smart cable prototypes.