That's WW1, bro.
Canada declared war in WW2 a week (to the day, iirc) after the UK. It was a deliberate political move by King, particularly due to the legacy of the Conservatives forcing conscription on Quebec after running on "no conscription" as a policy platform, permanently damaging the Cons electability in Quebec. By putting the view to parliament, and not whipping the Liberals to view fire declaring war, insulated the Liberals from political backlash from Quebec and asserted Canada's independence as a nation (which plays well in Quebec, in particular, ironically.)