A nearly $6-billion hostile takeover battle between two Canadian infrastructure giants—asset buyer Brookfield Infrastructure Partners and natural gas extractor-transporter Inter Pipeline—just got more expensive, with the Alberta government's new financial stake, observers say.

The government intervention comes as French water and waste management giant Veolia Environment SA's uninvited $13.1-billion bid to acquire its smaller but still sizable Paris-based rival Suez SA faces new obstacles from the intended target and regulators