In this paper, we investigate a new communication system architecture for ERTMS/ETCS, the most advanced standard for managing and controlling of railway traffic, integrating Public Land Mobile Networks (PLMNs), usually offering best-effort packet services only, with a Quality of Service (QoS) guaranteed satellite network, as a cost-effective substitution for dedicated 4G and 5G networks that should replace GSM-R, the current standard now at the end of its life cycle. Integration among those heterogeneous networks is provided by the Multi-path TCP protocol (MPTCP). As illustrated in the paper, proper setting of MPTCP add and drop subflow and priority handling logics allows to realize an efficient seamless vertical handover, compliant with railway requirements concerning availability, throughput, and latency.