There is indeed a vast swath of Canada which is crown land. Most of it is in the North of the country. According to this web site it is indeed more than 90% of the land. But bear in mind that most if it is either forest, tundra or ice.
The province of Ontario maintains a web site which gives your more information.
The interesting part of the text might be this:
Crown land is no longer actively marketed, rented or sold for private
recreational or residential use.
Using search engines revealed several sources. It definitely seems that you have to go to the provinces. Saskatchewan and Manitoba have at least the subject of land lease for agriculture on their web sites.
It seems you have to be Permanent Resident or Citizen to farm here.