> claiming that the USA had nowhere near the involvement they are credited with in WWII and that instead mainly Canadians stormed the Normandy beaches, is this true at all?
Not in the slightest; speaking as a Canadian, this is a VERY bad take given that two US Airborne Divisions landed in Normandy on the night of June 5th-6th 1944, and that three US infantry Divisions landed at Utah and Omaha beaches on the morning of the 6th, compared to one Canadian Infantry Division.
> Did one country contribute more than the other?
If one country did, it was Britain; British and Commonwealth warships were 75% of the naval forces assembled for Operation Neptune (the amphibious landing phase of Operation Overlord), and British forces captured two beaches (Gold and Sword) and took part in the airborne landings the night before (6th Airborne Division).
It's an unfortunate tendency that people can get into, that when familiar historical narratives that have been oversimplified are found to be flawed, people will lurch to the opposite extreme rather than seeking out a wider variety of sources to obtain a clearer picture of events. "The USA were back to back World War champs" becomes "USA did nothing to win the war," the Soviet Union's partially self-imposed marginalization in popular narratives of the war becomes "Western Allies did nothing, Ivan won all by his lonesome." American media will tend to focus on American aspects of events, for the same reason you'll hear about Canada's successes at Vimy Ridge, and hear next to nothing about the British and Australian contributions to the wider Battle of Arras in 1917. Most official histories of the world wars are national histories; they draw substantially from the records of allied and opposing countries, but their primary focus is on the armed forces of their particular state/government.
I'll leave you some sources for example: Joseph Schull's The Far Distant Ships, Canada's official postwar naval history, and Volume III, Part II of Stephen Roskill's The War At Sea, Britain's Official Naval History. They have good info on the subject you ask about, just bear in mind their purpose and perspective.