What date did Canada enter World War 1?

On 4 August 1914 Britain declared war on behalf of the whole British Empire.

It was actually on 5 August. The Germans entered Belgium on 4 August. Belgiums neutrality was guaranteed by a treaty signed by France, Britain and Germany and although Germany didn't believe that Britain and France wouldn't mind if Belgium was attacked ... they did! Great Britain declared war on 5 Aug on behalf of the entire British Empire.

On August 5, 1914, the Governor General of Canada, after being Directed by The Parliament of Canada Declared a war between Canada and Germany.