Here are key facts about the five largest:

CANADA PENSION PLAN INVESTMENT BOARD

* The CPP Investment Board was incorporated as a federal government corporation in December 1997 and made its first investment in March 1999. Its official mission is to maximize investment returns for Canada's public pension plan.

* The CPPIB invests funds not needed by the Canada Pension Plan to pay current benefits on behalf of 17 million contributors and beneficiaries.

* The CPPIB expects to have C$275 billion ($270 billion) in net assets by 2020 and over C$1 trillion by 2050.

* In 2011, the board more than tripled its investment in Internet phone service Skype in an $8.5 billion deal with Microsoft Corp. CPPIB took home $933 million less than two years after an initial $300 million investment.

* In 2010, in conjunction with Onex Corp, CPPIB was involved in the largest global private equity deal of the year, with the C$5.0 billion leveraged buyout of Tomkins Plc, a British maker of car parts, industrial hoses and bath tubs.

ONTARIO TEACHERS' PENSION PLAN

* With C$107.5 billion in net assets as of December 31, the Ontario Teachers' Pension Plan is the largest single-profession pension fund in Canada. It invests on behalf of 295,000 active and retired teachers in Ontario.

* In existence since 1917, the OTTP became independently administered in 1990 with the establishment of a nine-member board and has earned the industry's highest absolute returns for the past 10 years.

* Funds from around the world - most recently New York City's $110 billion pension fund - are trying to mimic Teachers' administration model, which emphasizes governance and professional management.

* Teachers' investments include a 48.25 percent stake in Birmingham International Airport, which it acquired in conjunction with Australia's Victorian Funds Management for C$875 million in 2007.

* Teachers' is among the world's most active pension fund investors in emerging markets. In July it spent C$541 million to raise its stake in two Chilean water utilities.

ONTARIO MUNICIPAL EMPLOYEES RETIREMENT SYSTEMS

* Established in 1962, the Ontario Municipal Employees Retirement System has about C$54 billion in net assets.

* In 2010, OMERS and Ontario Teachers' partnered on the 2.1 billion pound ($3.2 billion) acquisition of High Speed 1, Britain's only high-speed rail link to the Channel Tunnel.

* OMERS has $10 billion invested in the United States, in both public and private markets.

* In July OMERS Private Equity announced a definitive agreement to acquire V.Group Ltd., a ship management and crew provision company, from Exponent Private Equity for an enterprise value of $520 million.

* In October OMERS became one of Canada's largest venture capital investors with the launch of OMERS Ventures, a C$180 million fund that will focus on North American technology, media, telecommunications, clean technology and life sciences.

CAISSE DE DEPOT ET PLACEMENT DU QUEBEC

* The Caisse de depot et placement du Quebec was established in 1965 to manage the funds of the province's public pension plan.

* The Caisse focused on bond investing before first entering Canadian stock markets and then foreign markets. Today it invests in fixed income, equity and other investments in Canada and abroad, with a growing percentage, 4.7 percent at last count, in emerging markets.

* In November the Montreal-based institution announced an $850 million deal to buy ConocoPhillips' 16.55 percent stake in Colonial Pipeline Co, the largest refined petroleum products pipeline in the United States.

* The Caisse's real estate business has C$40 billion in assets, making it one of the world's 10 largest global real estate investors.

* Its infrastructure division owns a 23.15 percent stake in BAA, which owns six British airports, including London Heathrow.

ALBERTA INVESTMENT MANAGEMENT CORP

* Best known as AimCo, Alberta Investment Management Corp is the youngest of the major Canadian pension funds. Established in 2008, it manages C$70 billion in assets for more than 300,000 public sector employees in the oil-rich province of Alberta.

* AimCo's chief executive, Leo de Bever, sees opportunity for investment internationally as cash-strapped governments look to the private sector to finance large infrastructure projects.

* In November, AimCo bought a 50 percent stake in Chile's second-largest electricity distributor, Grupo Saesa, from Morgan Stanley Infrastructure Partners. In December 2010 it bought a 50 percent stake in Autopista Central, a six-lane toll road in the capital, Santiago

* In January 2011, together with the Australia New Zealand Forest Fund, AimCo completed the C$415 million acquisition of timberland assets from Great Southern Plantations.

($1=$1.02 Canadian)

(Reporting By Pav Jordan; editing by Rob Wilson)