Canadian Solar, based in Guelph, Ont., makes solar panels used to convert the sun's power into electricity and also builds and sells utility-scale solar electricity projects for investors.
Calgary-based TransCanada is best-known for its North American pipeline business but it's also active in power generation.
One of the new solar power facilities is in Ingleside, southeast of Ottawa, and two are in the New Liskeard region, about 160 kilometres north of North Bay.
The power stations have 20-year power purchase agreements with the Ontario Power Authority.
TransCanada previously bought four other solar plants from Canadian Solar. It says the seven solar farms are expected to generate enough electricity for more than 12,000 homes.
Canadian Solar said the TransCanada deal brings the total number of project sales during the third quarter to five.