Successful countries provide economy and society with infrastructure needed to maintain growth. Over the last decade, the Government of Vietnam has maintained high level of infrastructure investment. However, the electricity shortage, the natural disasters and the emission of greenhouse gasses still have been challenges that Vietnam has to confront to sustain high economic growth in the long term. Japan, one of the most developed nations, is moving forward aggressively to become a major global player in Smart Cities. For this reason, we focus on this promising `Smart City' project for considering the investment in Vietnam. This project requires huge investment financial amounts and long term to profitability under uncertainty. Hence, Public-Private Partnership (PPP) is an attractive scheme to optimize the trade-off between Vietnamese government-owned corporation (seeking for technology and capital) and foreign private firms (for market demand and regulation knowledge). In a context of a strategic partnership as a coopetition method, how the option-games as a methodology can find the optimality on the trade-off between flexibility and commitment for irreversible investment under uncertainty and competitiveness. Then the result is proposed to value the boundary of cooperate investment opportunities for both sides in this project.