Newspapers.com is a major resource

Digitized newspaper site newspapers.com, owned by Ancestry.com, has been adding significant Canadian content, the latest being 23 years of the Whitehorse Daily Star, from 1995 to 2017. While still weighted to the US, Canadian coverage of 76 titles is now comparable with that for California which has a larger population.
Within Canada, coverage favours the Western provinces.
There are 44 papers from British Columbia, three of which extend for more than a century: The Nanaimo Daily News, Chilliwack Progress and Vancouver Sun.
The 12 Alberta newspapers include 132 years of the Calgary Herald and 111 years for the Red Deer Advocate.
While there are only 6 Saskatchewan papers they include 137 years of the Regina Leader-Post and 118 for the Saskatoon Star-Phoenix.
Moving east, Manitoba is represented by 7 papers including 60 years of the Winnipeg Tribune starting in 1890 and 58 years of the Manitoba Free Press starting in 1874.
Ontario lists 5 titles. Ottawa is covered by the Daily Citizen for 1846 to 1897 and the Citizen for 1898 to 2019 — both together constitute the longest run, 174 years. The Ottawa Journal is available for 1885 to 1980. The Windsor Star has coverage from 1893 to 2019 and the National Post/Financial Post for 1907 to 2019.
Quebec has a single title, 163 years of the Montreal Gazette 1857 to 2019.
Newspapers.com has no coverage in the Atlantic provinces.

Much of the new content is from Postmedia. Access requires a premium subscription to newspapers.com. It may be that revenue from the digitized archive is helping in a small way to stem the company net loss which decreased to $7.7 million in the quarter ended 31 May, 2019 from $15.5 million in the same period in the prior year. Postmedia holdings not yet available include the Edmonton Journal, London Free Press and numerous smaller publications the archives of which will be of considerable interest for family history for the years when Canada's population was more rural and local newspapers had extensive coverage of social happenings.

Where could newspaper.com, or any other organization look for additional content? Opportunities would include the Irving-owned Brunswick Group newspapers including the Saint JohnTelegraph-Journal, Moncton Times & Transcript and Fredericton Daily Gleaner. The SaltWire Network owns the Halifax Chronicle-Herald, Charlottetown Guardian and St John's Telegram among many other Atlantic Canada newspapers.

In Quebec it appears the Thompson organization owns the archive of the Montreal Star, for much of its 110 years the city's leading English language paper.