Canadian police mass in the capital, readying to clear a trucker-led protest that has choked Ottawa's streets and provoked the government to call on rarely-used emergency powers. With barricades going up overnight and a heavy police presence forming in the area where hundreds of big rigs remain parked, Prime Minister Justin Trudeau was in Parliament nearby defending his decision to invoke the Emergencies Act for only the second time in peacetime. IMAGES AND SOUNDBITES