It's one of the things that makes the attempts of Len Rodness to bring a copy of the Magna Carta to Canada so interesting. (see this article in the Star about it.)What would we make of it now?
The Magna Carta was the agreement signed by England's King John 1 in 1215 with the barons of his realm who rose up in rebellion and essentially forced him to sign an agreement limiting his powers. The medieval terms of the agreement were fairly narrow, but in later years it came to be part of an invented tradition of democracy in Britain, each generation using it to expand the democratic powers of parliament, a document that became powerful precisely because of its history and because it showed a very long standing tradition of limiting royal power (however limited the initial premise).
In bygone generations, English Canadians would have understood the Magna Carta as part of the British parliamentary legacy - part of the British tradition of liberty and fair play (with all of its omissions that often weren't acknowledged) that Canada inherited. In the 1950s when Liberals were busy demolishing the British symbols in Canada, much to the delight of French Canadian nationalists, and increasingly as many English Canadians didn't especially notice or bother about it, Eugene Forsey railed in indignation when Arthur Lower complained about how English Canadians took such things like the Magna Cart as a 'tradition not thine own.'
This, to Forsey, was nonsense. It was his tradition. It was the tradition of Canada.
What would we think now?
Personally, I first heard of it when I was a young voracious reader of about eleven, poring through the historical novels of Sharon Kay Penman. Good reading still, though I can't find an image from the edition I read.