There is no single comprehensive source for American and Canadian newspapers. In some cases you will need to look at one website for current and recent issues of a newspaper eg Nexis and at a different website to look at older issues of the same newspaper. Some websites are free, others can be searched for free but require you to pay to read the articles you find, and others require you to take out a subscription to search them.
Websites to help you find American and Canadian newspapers
Directory of Historical Newspapers on the Internet
Links to various newspaper archives, arranged via state. Includes both fee paying and free resources.
Chronicling America: Historic American Newspapers
contains the U.S. Newspaper Directory which gives publication details of American newspapers published between 1690 and the present, as well as the full text of selected historical newspapers from the period 1836-1922
Pay to use service containing wide range of digitized papers
Archives of newspapers:
African American Newspapers, Series 1, 1827-1998. This collection includes more than 280 newspapers from 35 US states. The newspapers are written for and by African Americans, and include Freedom's Journal, which was the first African American newspaper in the US.
Brooklyn Daily Eagle Online, 1841-1902
Canadian Newsstream. This database offers access to the full text of over 190 Canadian newspapers from Canada's leading publishers. This full text database includes the complete available electronic backfile for most newspapers, providing full access to the articles, columns, editorials and features published in each. Some backfiles date as far back as the late 1970s.
ProQuest Historical Newspapers: Chicago Tribune (1849-1994)
Full-text searchable database part of ProQuest Historical Newspapers through FindIt.
New York Times
Keyword searchable archive of articles from the New York Times since 1851.
Note: Articles from years 1923-1986 are not free of charge.
U.S. Newsstream. Enables users to search the most recent U.S. news content, as well as archives which stretch back into the 1980s featuring newspapers, newswires, blogs and news sites in active full-text format. It offers one of the largest collections of local and regional newspapers, including the Los Angeles Times, Chicago Tribune and The Wall Street Journal, and is cross-searchable on the ProQuest platform.
Washington Post, 1877-2005.