The self-imposed blackout is a protest against proposed anti-piracy legislation in the United States that could have far-reaching effects for Internet users and companies around the world.
The Stop Online Piracy Act and the PROTECT IP Act could allow website addresses to be blocked when complaints are filed about copyright infringement.
Search engines and websites could be compelled to remove links to sites accused of copyright violations, and web payment processors and advertisers could be forced to stop doing business with alleged offenders.
"These legislative proposals by their design will have an impact in Canada," said University of Ottawa Prof. Michael Geist, Canada's Research Chair in Internet and E-commerce Law, who plans to black out his blog Wednesday.
"Any Canadian website owner could in theory find themselves subject to a court order in the United States and ISPs would be required to block them, and search engines would be required to remove them from their listings, all without their participation in a hearing.
"I think it's enormously problematic."
Tucows (TSX:TC), a Toronto-based company that manages over 11 million domain names and provides other Internet services, is planning to temporarily take down its popular downloading site, which hosts more than 40,000 programs.
The U.S. legislation could theoretically affect Tucows if someone claimed it was allowing downloads of software illegally.
"There will be hundreds of thousands — maybe a million — people impacted by not being able to download the software they want but we feel it's important," said Ken Schafer, executive vice president of products for Tucows.
"It's not just about inconveniencing them, it's about getting to those people and making them aware of this issue and getting them to take action."
Social media service Identi.ca is also among the Canadian sites joining the likes of Boing Boing, Reddit and Wordpress in the protest. Google plans to place a link on its home page proclaiming their opposition to the U.S. bills.
Only the English portion of Wikipedia is going offline Wednesday, reads a message to users signed by Canadian Sue Gardner, executive director of the Wikimedia Foundation.
"My hope is that when Wikipedia shuts down on Jan. 18, people will understand that we're doing it for our readers. We support everyone's right to freedom of thought and freedom of expression," she wrote.
"We believe in a free and open Internet where information can be shared without impediment. We believe that new proposed laws like SOPA and PIPA, and other similar laws under discussion inside and outside the United States, don't advance the interests of the general public."