Recent advances in music recording and dissemination (cheap home
recording and the internet) mean that more artists can record and
distribute their music than ever. Canadian pop music is experiencing
high critical acclaim at home and (particularly) abroad. Why are some
of the most acclaimed Canadian artists (e.g. Broken Social Scene,
Feist, The New Pornographers, K?naan, Corb Lund, Buck 65, Stars,
Caribou, Arcade Fire ?) largely ignored from commercial radio and
television?

NOTE: for this question, it would be helpful to get information from
academic websites, academic journals, and/or newspaper articles. 
Also, I need the citations for these sources

I will leave it to a registered expert to give you the sources you
need for your paper but I will comment on your question. The
independent artists you have named are part of a movement that is
building outside of the traditional mainstream. There is a quote I can
give you;  "I believe we could be seeing a paradigm shift from the
domination of the ?music business? to that of the ?musician business?.
John Perry Barlow  Many of the artists you named pride themselves on
being out of the "mainstream" music business including commercial
radio. Arcade Fire has been nominated for a Grammy without all of the
attendant machinery of big business. So, my answer to you is that they
don't need and they spurn the traditional routes of exposure once
sought so frantically. For their part, radio and television are in the
advertising business, not the music business. They play whatever will
draw the demographics that they are selling to their advertising
clients. The demographics that you have identified by the groups you
have named, are not likely to be tuning in to the stations that play
commercial music and indeed, some of their fans might well be turned
off by hearing their favorite act on one of the mainstream stations.
So, the system is working from recording to dissemination to financial
and critical success outside the "system". There is a new way of doing
business that puts the art first and for those of us old enough to
remember.... that is how it used to be as well.

Like terrymac just a comment :

The payola system is still very much alive and would prevent many such
artists from getting air play.

http://news.google.com/news?hl=en&ned=us&q=payola+sony&ie=UTF-8&scoring=d