(Corrects ownership of Arlanda Express stake in final paragraph)
LONDON, July 28 (Reuters) - Canada's Ontario Teachers' Pension Plan is seeking to buy the rest of Britain's Bristol Airport in a deal worth up to 250 million pounds ($424.6 million), a source closely monitoring the situation said on Monday.
The pension fund, which already owns 49 percent of the regional airport, has the right of first offer for the 50 percent owned by Australian asset manager Macquarie Group .
Macquarie, the world's largest infrastructure asset manager, was sounding out buyers for its holding, British newspaper The Sunday Times reported.
Ontario Teachers' Pension Plan is eyeing the stake as it seeks to expand its infrastructure holdings from $12 billion to around $18 billion. The deal could take place this year, the source said.
"Given the right of first offer, Ontario Teachers is likely to purchase the stake, but this will of course be based on an appropriate valuation," the source said, adding that discussions have not commenced but are expected to start "very soon".
European airport deals typically attract a valuation of 15-17 times core earnings (EBITDA).
Macquarie holds its stake in Bristol Airport, the country's ninth-busiest, as part of its 2004 Macquarie European Infrastructure Fund (MEIF). The company was not immediately available for comment. Sydney Airport holds the remaining 1 percent.
Ontario Teachers, which also has a stake in Birmingham Airport, originally invested in Bristol Airport in the south-west of Britain in 2002 and increased its stake in 2009.
The 1.5 billion-euro MEIF is coming to the end of its life cycle, so Macquarie will either have to sell its holdings and return money to investors or seek their permission to roll them over into its second or third infrastructure funds.
The MEIF sold its holding in Swedish high-speed rail service Arlanda Express in July and owns stakes in UK ferry company Wightlink Shipping and Brussels Airport. ($1 = 0.5888 British Pounds) (Reporting By Freya Berry; Editing by Lisa Jucca and Erica Billingham)