SAO PAULO, Dec 28 (Reuters) - Engie Brasil, the Brazilian subsidiary of France's Engie, said on Thursday its board of directors approved the sale of a 15% stake in natural gas pipeline firm TAG to Canadian investment fund Caisse de Depot et Placement du Quebec (CDPQ) for 3.11 billion reais ($641.22 million).

After the conclusion of the deal, Engie Brasil will still hold a 17.5% stake in TAG, remaining in its controlling group with CDPQ and GDF International. ($1 = 4.8501 reais) (Reporting by Peter Frontini Editing by Chris Reese)