The best choice from the given options would be:
A. Escalate the issue to the sponsor and ask for stakeholder engagement.
In this scenario, the project is facing a significant strategic transition, and there's disagreement among stakeholders about this transformation. The project manager, who is responsible for executing the project but not for making strategic decisions, should escalate the issue to the project sponsor or other appropriate decision-makers.
These decision-makers can then engage with the stakeholders, understand their concerns, and try to reach a consensus or make decisions that balance the various stakeholders' interests. This may also involve revisiting the project's business case and strategic alignment.
Option B, reviewing the project business case and updating it periodically, is a good practice in general, but it may not directly address the current issue of stakeholder disagreement.