The investment arm of Canada Pension Plan yesterday offered to buy Australian toll-road operator Intoll Group for A$3.47 billion ($3.1 billion), its second attempt to buy the company that is backed by the Macquarie Group.

The offer from Canada's second-biggest pension manager sent the Sydney-based Intoll's shares soaring by more than 30 per cent in yesterday's trading close at the Sydney Stock Exchange.

Canada Pension Plan Investment Board (CPPIB), valued at around $6.4 billion, has offered A$1.535 for each Intoll share, 42 cents more or 38 per cent higher than Intoll's closing price yesterday.

CPPIB said it will give Intoll shareholders a choice of cash for each Intoll share, or one unlisted share in one or more newly formed acquisition entities for each Intoll share or a combination of the above alternatives.

''The directors of Intoll have not formed a view as to the adequacy of the Proposal and accordingly recommend that Intoll security holders take no action at this time,'' said Paul McClintock, chairman of Intoll.

The board of Intoll however has agreed to CPPIB request of conducting due diligence for a three-week period and it has not asked to be granted exclusive due diligence.

"We believe Intoll's toll road assets are a good fit with CPPIB's portfolio and long-term investment mandate, and are well-situated strategically to benefit from future urban growth in Toronto and Sydney," said CPPIB's executive Andre Bourbonnais.

Macquarie Infrastructure Group, which spun of Intoll into a separate company in January 2010, still holds an 18 per cent stake in Intoll, while asset management firm Lazard & Co holds 10.5 per cent and Abu Dhabi Investment Authority holds 9.9 per cent.

Intoll currently holds a 30-per cent interest in the 407 ETR (toll road) in Toronto, Canada and 25 per cent in Westlink M7 in Sydney, Australia, but the majority of Intoll's revenue comes from Toronto 407 ETR.

Early this year, CPPIB had teamed up with Canada's largest pension plan Ontario Teachers to make an unsuccessful A$3.7 billion bid for Australian toll-road group Transurban.

Transurban had rejected the offer and instead went for a share sale.