Infrastructure funds InfraRed and EIP are also close to making offers, the source said.
Europe's largest utility is holding calls with the prospective buyers for the minority stake of the wind farm, two sources said, and it will select a winner in coming weeks.
Iberdrola, InfraRed and EIP declined to comment while Masdar and CPPIB could not immediately be reached for comment by Reuters outside regular business hours.
Iberdrola is selling stakes in its wind developments to investment funds to help finance its 150 billion euro 2020-2030 investment plan, mostly devoted to renewables and power grids.
It sold 40% of a British development to Macquarie's Green Investment Group in 2019.
Bank of America and Santander are managing the Wikinger sale which they expect to close before the end of 2022.
Iberdrola expects to end the year with 46 billion euros in debt, higher than its 44 billion euro projected revenue. This calculation does not include any asset disposals, Chief Financial Officer Jose Sainz said last week.
Wikinger is part of the so-called Baltic hub located off the island of Rügen. It started to produce energy in 2018. When the three wind farms at the site are finished in 2026, they will have more than 1,100 MW of installed capacity.
One gigawatt is roughly equal to two coal-fired power plants. Iberdrola says Wikinger provides the equivalent of one year consumption of electricity to approximately 350,000 homes.
The Baltic Hub is expected to cost a total 3.5 billion euros.
Harnessing powerful wind speeds offshore is key to many governments' plans to wean themselves off fossil fuels and reduce dependence on imports, a quest which has gained urgency in Europe since major producer Russia's invasion of Ukraine.
Iberdrola has 1,258 MW offshore in operation and 5,500 MW under construction, and it calculates it will have invested around 30 billion euros worldwide in turbines planted off windy coastlines by 2030.
(Reporting by Andres Gonzalez, editing by Nick Macfie)
By Andres Gonzalez and Isla Binnie