The rapid expansion of the Internet of Things (IoT) has intensified demands for scalable traffic management, real-time visibility, and resilient control in large, heterogeneous networks. Conventional Software-Defined Networking (SDN) architectures, typically based on centralized control and static forwarding, struggle to address the dynamic, data-intensive behavior of Software-Defined IoT (SD-IoT) systems. To overcome these limitations, this paper proposes MC-LBTO, a modular multi-controller framework that integrates programmable data plane intelligence with adaptive, secure coordination among distributed controllers to optimize load balancing and network efficiency. MC-LBTO comprises three cooperative modules: PDSM (P4-enabled Dynamic State Monitoring) for in-switch traffic observation and analytics; PALB (P4-based Adaptive Load Balancer) for latency-aware and fair traffic distribution; and STAM …