This study explores the application of blockchain technology to enhance scalability and security in multi-cloud communication systems. Current centralized security methods in multi-cloud environments often suffer from high computational complexity and limited scalability. By conducting a comparative analysis of various blockchain implementations: including Proof of Work (PoW), Proof of Stake (PoS), Byzantine Fault Tolerance (BFT), and sharding: we evaluate their performance in terms of scalability, computational complexity, latency, and energy consumption. The findings reveal that integrating blockchain mechanisms like PoS and sharding can significantly optimize multi-cloud communication. We propose an optimized blockchain-based framework that balances energy efficiency with enhanced scalability and security, aiming to address the identified gaps in existing systems.