PORTLAND – TD Banknorth could benefit if its parent company sells some or all of its stake in a discount stock brokerage, a stock analyst said.

TD Bank, a Toronto-based financial institution that owns 51 percent of Portland-based TD Banknorth, said this week that it is talking to online brokerage Ameritrade about a possible transaction involving TD Waterhouse, the stock brokerage owned by TD Bank.

The companies plan no further comment until the talks conclude, but reports said the deal would be worth as much as $3 billion.

A sale of some or all of TD Waterhouse “would clearly free up capital that could be used to help Banknorth grow its banking platform in the United States,” said Jim Ackor, an analyst who follows TD Banknorth for RBC Capital Markets in Portland.

Banknorth owns some 400 banks and 550 ATMs in Maine, New Hampshire, Massachusetts, Connecticut, Vermont and upstate New York. Bank officials have said they intend to expand operations in New England and possibly in New York.

Ackor said TD Bank could use proceeds from a TD Waterhouse transaction to buy more TD Banknorth stock or to help TD Banknorth buy other banks. Before being acquired by TD Bank earlier this year, TD Banknorth had bought 26 banks in the 11 previous years.

TD Banknorth President and CEO William Ryan has said he wants to beef up the bank’s presence in the Boston and southern Connecticut markets, and is interested in opportunities to move into either New York City or a nearby market.

“They will look at pretty much anything in southern New England, and there

are franchises that make a great deal of sense in the New York market as well,” Ackor said.