This paper examines the interplay between the information strategy of an e‐commerce platform and the selling mode strategy of a manufacturer within a co‐opetitive supply chain, as well as the identification of the optimal supply chain strategy. We develop a supply chain model where a platform outsources production of its private label product to a manufacturer, who also sells its national brand product through the platform. The platform must decide whether to acquire consumer quality preference information at a cost and share it with the manufacturer, while the manufacturer needs to choose between the reselling mode or the agency selling mode for its national brand product. The two driving effects (competition‐intensification effect and mode differentiation effect) are identified. Our findings show that the platform will acquire and share information when the acquisition cost is sufficiently low, leading to the “competition‐intensification effect.” Additionally, the manufacturer prefers the agency selling mode when cost‐quality efficiency is low, and the reselling mode otherwise, driven by the “mode differentiation effect.” In cases where information sharing is absent, the manufacturer is more likely to choose the agency selling mode. Interestingly, when the cost‐quality efficiency of the manufacturer's product is moderate and the information acquisition cost is low, the “competition‐intensification effect” and the “mode differentiation effect” offset each other, resulting in the expansion of the region where the manufacturer chooses the reselling mode due to the platform's information‐sharing strategy. As a result, this enhances a cooperative relationship between the manufacturer and the platform. We also derive the optimal supply chain strategy, providing insights into both the manufacturer's selling mode and the platform's information strategies in online retailing.