Why is there not a Canadian flag emoji?

A mechanism for providing ALL flags was developed years ago, using "Regional Character Pairs". It is sheer laziness by Apple not to have provided all flags. It is not difficult to do. This grid shows all the defined flags, and those not defined: http://www.chris-ward.pwp.blueyonder.co.uk/emoji_flag_grid.htm

You need to be using browser that supports emoji (such as Safari)

There is character 1F341
which is probably the best Canadian emoji symbol until somebody gets their finger out…

The language used on that site is somewhat misleading. All flags are in fact "defined" -- it's known exactly where on the grid they should be placed. Canada is at 1f1e8 1f1e6. It is just a question of whether someone has made font which includes all the flag glyphs at those locations. Apple has not devoted any effort to that, but perhaps someone else has.