UPDATE 4-TransCanada in talks to buy Columbia Pipeline Group - sources
* TransCanada says in discussions for a potential deal
* Columbia Pipeline valued at about $8 bln as of Wednesday's close
* Columbia Pipeline shares up 16.6 pct in afternoon trading
* TransCanada stock down 3.2 pct in Toronto; 4 pct in U.S. (Adds deal details from source)
By Mike Stone
March 10 (Reuters) - TransCanada Corp, the company behind the controversial Keystone XL oil pipeline project, is in talks to buy U.S. natural gas pipeline operator Columbia Pipeline Group Inc, two people familiar with the matter told Reuters.
The two companies have so far failed to agree on a price, and a deal remains uncertain, one of the sources said.
TransCanada said in a statement it was in discussions with a third party for a potential transaction, but no agreement had been reached.