Did Canada have a large or small effect on the D-Day invasion of Normandy?

"Effect" is a relative term which is subject to opinion. Canada, with one decision, did have the third largest contingent of troops participating in the assaults. The Canadians under the command of Maj.-Gen. R.F.L.Keller were responsible for Juno beach in the center of the British front, tasked to establish a beachhead on a 5 miles front. they pushed further inland than the British or Americans against very fierce resistance to reach Carpiquet airfield 11 miles in by nightfall.The 1st Canadian Para Battalion dropped with the British 6th Airborne on the left flank and destroyed all their assigned targets and wreaked havoc behind the German lines.Approx. 14,000 Canadians landed and sustained 1,074 casualties,of which 359 were fatal. But that was only day #1, they went on to liberate Holland and capture the Sheldt ,no mean feat. the invasion went ashore along lanes swept clear of mines by the Canadian navy, and the Canadian airforce had bombers hitting German batteries while its fighters were hammering targets inland.Yes ! Canadian forces were very "effective".