French real estate group Unibail-Rodamco said it signed an agreement to sell a 46.1 percent stake in German shopping centre operator mfi AG to the Canada Pension Plan Investment Board (CPPIB) for 394 million euros ($450 million).

The move extends an existing German joint venture between Unibail and CPPIB created when Unibail took a stake in the CentrO shopping centre in Oberhausen a year ago.

"As a long-term investor, this transaction provides us with the unique opportunity to achieve immediate scale in the retail sector in Europe's largest economy," CPPIB Managing Director and European real estate investment head Andrea Orlandi said in a statement.

Unibail-Rodamco's stake in mfi of 94.15 percent will fall to 48 percent following the transaction, which is expected to close in the third quarter, the company said.

CPPIB meanwhile will appoint two representatives to the supervisory board of mfi and will invest a further 366 million euros to support mfi, the companies said.

The impact of the proposed deal was "anticipated and is included in the 2015 full-year recurring earnings per share guidance" that Unibail gave in January, the company said in the joint statement.