In response to the growing importance of negotiations in today's complex business environment, we examined the effectiveness of an interactive negotiation canvas aimed at upskilling inexperienced negotiators through AI to improve negotiation outcomes. Building on prior research linking preparation to negotiation success, we introduced an interactive canvas to assist negotiators. We evaluated the canvas in an online experiment with 108 participants who prepared for negotiations using the interactive canvas or a common planning guide. Subsequently, participants negotiated with an LLM-based conversational agent (representing the negotiation partner), allowing for a comprehensive evaluation of the preparation methods. Results show that participants using the interactive negotiation canvas achieved significantly higher negotiation outcomes with a more balanced cognitive load than the control group. These findings highlight the effectiveness of structured, interactive preparation tools in optimizing negotiation performance and underscore the importance of adapting content presentation to improve user experience and outcomes in negotiation settings.