Warning:
Canada's WESTJET airline advises that persons traveling with their violin or viola may be asked to surrender their instrument to baggage. It is at the discretion of the counter clerk. If damage has occurred, you have only 24 hours to file a claim, which is limited to $250 maximum in Canadian funds.

The United States Department of Transport  issued the following letter dated January 17, 2003 as regards their policy of hand-carried instruments. It is also listed here as a word document of you wish to print it.