Sept 20 (Reuters) - A consortium led by Australia's Transurban Group will pay A$11.1 billion ($8.06 billion) for a near half stake of the country's longest auto tunnel network, giving it full ownership of the asset and dominance of Sydney's toll road network.

Transurban already owned 51% of WestConnex, a roughly 70 kilometre (44 mile) system of toll roads linking Sydney's sprawling metro area, along with Canada Pension Plan Investment Board, Abu Dhabi Investment Authority and domestic pension fund AustralianSuper. The New South Wales state government owned the remaining share.

Buying out the 49% share from the state gives the group - of which Transurban owns a half share - the full financial benefit as more sections of the giant capital works project open to traffic in the next few years. The consortium added Canada's Caisse de dépôt et placement du Québec as a member, Transurban added.

"WestConnex is one of the largest road infrastructure projects in the world (and) a key component of the New South Wales government's integrated transport plan to ease congestion and connect communities in Sydney," said Transurban CEO Scott Charlton in a statement.

"We feel privileged to take Sydney Transport Partners' holding in this critical asset to 100%," he added, using the name of the consortium.

Transurban said it would raise A$4.22 billion in a stock issue to fund its part of the purchase, which already had the necessary regulatory approval. The company owns most Sydney toll roads and dominates Australia's toll road market from coast to coast.

Australia has been experiencing a spike in mergers and acquisitions activity over the past year as lockdowns put downward pressure on asset valuations while rock-bottom interest rates make it cheaper for investors to raise capital.

Also on Monday, power grid owner AusNet Services Ltd said it would open its books to Canadian investment giant Brookfield Asset Management after it made a A$9.6 billion indicative offer.

($1 = 1.3772 Australian dollars) (Reporting by Byron Kaye in Sydney, Sameer Manekar in Bengaluru; Editing by Diane Craft and Sam Holmes)