The reason the Canadian flag is so well recognised is that it is so simple and uncluttered, displaying the maple leaf as it does.
And I still maintain it isn't really what's on the flag, it's how much it's out there. The Canadian flag could still have a Union Jack in the corner, and 5 ice hockey pucks on it and still be just as recognised as the Canadian flag if it was as prevalent as the maple leaf one is. People only know it as the Canadian flag if they are worldly enough to recognize and equate a maple leaf with a particular country. Look at the Union Jack, nothing about it directly tells you what country it represents, but because of its overwhelming presence, most people will know. Same as the US because it is everywhere. Japan, a red disc on a white background - what says Japan about that? Unless you already know it is Japan's flag, there's no clue. The French flag? What the hell says France about that? Maybe they should put the Eiffel tower on it instead?
Have a look at the Norfolk Island flag, just a clean green Norfolk Island Pine on a green and white three panel flag.
And only the 3 people who live there would have any clue what they were looking at. It doesn't say Norfolk Island to anyone else.
Flags have meaning to the people who live under them. It isn't about making up for other people's ignorance. Do we have to be reduced to pictograms to pander to the lowest common denominator?