Polymarket, a U.S.-based prediction-market website, is taking wagers on who will be London, Ont.’s next mayor. There are also markets for Toronto, Windsor and even Stratford. The past two years have seen commercial prediction markets move from a niche forecasting tool into mainstream finance, allowing users to buy and sell contracts tied to the outcomes of real-world events ranging from elections to economic indicators. A 2024 U.S. federal court…