Aug 8 (Reuters) - Bank of Nova Scotia, Canada's third-biggest lender, said on Thursday it would record a C$300 million ($226 million) gain by reducing its stake in Thailand's Thanachart Bank Public Co (TBank).

TMB Bank had agreed in February to merge with TBank in a deal worth up to 140 billion baht ($4.55 billion), making the new entity the sixth-largest bank in Thailand.

Scotiabank's stake sale was part of the merger deal between TBank and Thailand's TMB Bank.

Scotiabank said it will cut its 49% interest in TBank and sell its interests in TBank in exchange for cash and shares in TMB.

Scotiabank expects to own about 6% of the new merged bank after the deal closes and will retain a 49% interest in two TBank units that are expected to be subsequently sold in 2020.

Scotiabank will also increase common equity Tier 1 ratio by about 25 basis points at closing of the deal, and said that it expects the future sale of its retained interest in the two TBank subsidiaries to result in an additional gain.

($1 = C$1.33) ($1 = 30.75 baht) (Reporting by Arundhati Sarkar in Bengaluru; Editing by Bernard Orr)