In both World War One and World War Two, food production in Canada was important to allied victory; in particular, reserves of grain from Canada and the USA's harvests in 1916 ensured that the British would have sufficient food during the German U-Boat Offensive of 1917.

Militarily, Canada's Navy made a significant contribution to the Battle of the Atlantic in WWII, possessing the World's 4th largest navy in 1945 (although this is more to do with the fact that the bulk of Germany, Japan, Italy and the USSR's navies were either at the bottom of the sea or mothballed). In production of military equipment and weapons, Canada supplied munitions, small arms, vehicles and aircraft, in particular the Canadian Military Pattern (CMP) truck used by the British Army. Commonwealth pilots trained at schools in Canada, and hundreds of Canadian officers served in the British Armed Forces, under the CANLOAN program.

On the ground, Canadian units made significant contributions in both World Wars. In WWI, 1st Canadian Division helped to halt the German attacks in the Ypres Salient during the Second Battle of Ypres in 1915. The Canadian Corps participated in the British attacks at Flers-Courcelettes and Thiepval in September 1916, and most famously captured Vimy Ridge in April 1917, securing the northern/left flank of the British 3rd Army. Canadian Cavalry Brigade nearly broke through the German lines at the Battle of Cambrai in November 1917, but British tanks and infantry collapsed the only bridge over the Canal du Nord, and poor command and control saw the Cavalry Corps committed late to the battle anyway. They fought most famously in 1918 at Moreuil Wood and Ridge in March, halting and repulsing lead elements of the German 18th Army, which contributed to the defeat of Operation Michael. The Brigade was subsequently involved in the successful attack at Amiens on August 8th, engaging in the cavalry assault that followed the initial attack, and which doubled the depth of the Allied penetration from 5000 to 10 000 yards. The Canadian Corps was a key part of this operation, possessing greater manpower and firepower probably than any other Corps in the BEF, save the Australians (who were increasingly a wasting asset, and were withdrawn in late September for rest). These actions at Amiens helped to maintain the momentum against the Germans already begun at the Second Battle of the Marne, and in September 1918 the Canadian Corps broke through the Hindenburg Line at Canal du Nord and through it's subsidiary, the Drocourt-Qeaunt Switch Line, thus helping to eject the Germans from their last prepared position in the west. From then on to the Armistice, the Canadian Corps played a high-profile role as the spearhead of Henry Horne's First British Army.

In World War II, Canadian divisions were involved in the Husky Landings in Sicily in 1943, and the Neptune/Overlord Landings in Normandy in 1944. In Italy, I Canadian Corps spearheaded 8th Army's advance in the Liri Valley late May 1944, which combined with attacks at Anzio and Monte Cassino lead to the liberation of Rome and the German retreat to the Gothic Line. After the Normandy Landings, the troops of what would become Canadian II Corps were engaged in fighting almost non-stop, suffering the heaviest losses in British Second Army. II Corps subsequently was responsible for the break in of the German positions at Falaise, Operation Totalize, and the subsequent exploitation and advance to the Seine. After this, the newly formed 1st Canadian Army was responsible for clearing the Channel Ports and the approaches to Antwerp, the latter task in particular being vital to the continued advance into Germany. Canadian 1st Army subsequently was chosen to conduct Operation Veritable, the offensive that lead to the crossings of the Rhine in Operation Varsity, and 1st Army (now commanding both Canadian Corps) was then responsible for ending German resistance in the Netherlands, bringing both relief to the starving population and an opening to the North Sea coast, where the Canadian forces ended the war.

In WWI, Canadian ground forces made an affect on Allied efforts at the tactical and operational level, while in WWII they were able to extend this into the strategic realm. It's worth noting that at it's best in 1918, Canadian Corps numbered close to 100 000 men, and with conscription and Arthur Currie's creation of a replacement pool, was well served in terms of reinforcements. 1st Canadian Army at it's largest, during Operation Varsity in which it commanded British XXX Corps, fluctuated around 145 000, and was subsequently far lower in strength before and afterwards. Like the British, they suffered from significant manpower shortages, but unlike the British, these could not be remedied with RAF and RN personnel. 1st Army fought through it's most important campaigns, along the channel, in the Schedlt Estuary, and in the Rhineland, chronically understrength, and in demoralizing conditions. Despite this, it was able to complete it's missions and contributed to the final Allied victory in Europe, grossly out of proportion to it's size.

If you want solid reading on both wars, I'd recommend Tim Cook's books At the Sharp End and Shock Troops, about the Canadian Corps, and Terry Copp's books Fields of Fire and Cinderella Army, about the Canadians in Normandy and Northwest Europe.