This study explores the structural certification challenges and business objectives for an electric seaplane in the general aviation category, emphasizing the verification of the composite structure under EASA CS-23. Sandwich structures and bonded joints offer significant weight reduction and structural efficiency advantages, crucial for electric aircraft. However, a fatigue damage and tolerance evaluation under CS-23 Level 4 increase these challenges, requiring exhaustive testing, analysis, and documentation to meet stringent regulatory standards. Certification complexities are further intensified by the differences in passenger capacity constraints between Level 3 and Level 4 aircraft, suggesting pursuing Level 3 certification and impacting on the business case of the emerging sustainable aviation. To evaluate the impact on the weight penalties, this study conducts a comprehensive FEM validation and comparison of two different CFRP wing structural analyses: one to comply with Level 3 certification using a monocoque sandwich structure with a bonded assembly, and the other to comply with Level 4 certification using semi-monocoque with a mechanically fastened assembly. The use of different strain allowable values for both levels defined the current strain constraints range for the composite wings, where the monocoque structure analysis showed a mass reduction of up to 19 % on average.