State immunity — Jurisdiction — Waiver — Development of concept of sovereign immunity at common law — State Immunity Act 1985 — United States of America commencing action in United States courts — Allegations of liability for environmental damage under United States environmental protection legislation — United States obtaining injunction in Canadian court freezing assets pending outcome of United States case — Undertaking in damages — Dissolution of injunction by Canadian court — Counterclaim seeking damages against United States and its functionaries pursuant to undertaking and common law tort claims — Whether United States immune from jurisdiction of Canadian court — Whether United States functionaries immune from jurisdiction of Canadian court — Relevance of whether functionaries’ immunity derivative or independent of sovereign’s immunity — Applicability of exceptions to general principle of sovereign immunity — Whether waiver of immunity — Whether Canadian court lacking jurisdiction simpliciter — Whether Canada forum non conveniens — The law of Canada