The dominant online platform (e.g., Amazon and JD) has introduced its private product following the manufacturer, transforming their relationship from cooperation to coopetition. The manufacturer, as the original seller of products, possesses a competitive advantage in the final product market, thereby, leaving a segment of uninformed consumers who only know manufacturer-launched products. Meanwhile, informed consumers may exhibit different preferences between the manufacturer and platform’s product. Thus, a critical challenge faced by the platform who introduces the private products is how to brand itself to maximize the profit while simultaneously balancing its cooperation with manufacturers. In addition to the product encroachment, the platform can decide whether to cooperate with manufacturers via either a reselling or agency selling channel. The channel structures significantly influence the profit of both parties. This raises another practical problem, how the platform should adjust its branding strategy across channels when facing with consumers having heterogeneous preferences. To address these practical challenges, we develop a game-theoretic model to investigate the platform's branding strategy under different channel structures. Specifically, if the platform decides to brand, the platform's branding efforts can convert potential buyers of a certain product into informed consumers and influence their utility. We then investigate the platform's optimal branding strategy across channels. Furthermore, we compare the platform’s and manufacturer's profit under different channels to investigate the platform's and the manufacturer's channel preference in case of branding and find that under certain conditions the channel preferences of both parties may coincide and a win-win situation can be achieved.