Air Canada's Washington DC based shyster explains their position thus:

"Air Canada does not object to the concept of criticism of its officers and directors, however, Air Canada does object to your unauthorized use of Air Canada's federally registered trademarks and...distinctive Web site trade dress."

In other words, "The only people allowed to heap scorn and shame on our brand is us, buddy."

The protest site is here—see for yourself how close it comes to confusing you with AirCanada.com. It's pretty clear that this is another example of corporations using intellectual "property" law to frustrate free speech that isn't to their liking.