Automaker General Motors Co plans to begin courting investors for its initial public offering immediately after the November 2 U.S. midterm congressional elections, two sources familiar with the plans said on Wednesday.

GM's roadshow is set to begin on November 3 and will last two weeks, the sources said. The IPO is expected to price on November 17 and debut on November 18, the sources said.

The sources cautioned that the plans were still being finalized and could change based on how U.S. stock markets perform.

Waiting until after the November 2 elections would also allow bankers to tout GM's third-quarter financial results to investors although the automaker has cautioned that the second half of the year will show a slowdown from the first half.

In August, GM filed paperwork for an IPO that could be worth as much as $20 billion, making it potentially one of the biggest IPOs of all time and the biggest new issue in the United States since Visa Inc's March 2008 IPO of $19.7 billion.

The final value of the IPO has not been set but one source said early plans for the IPO envisioned selling $12 billion to $16 billion in common stock and $3 billion to $4 billion in preferred stock that would convert to common stock under a mandatory provision.

GM filed paperwork for its IPO just over a year after emerging from a government-sponsored restructuring in bankruptcy. The U.S. government poured $50 billion of taxpayer money into the carmaker and emerged with a 61 percent stake.

Despite its success in preventing the liquidation of GM and Chrysler that many analysts had feared, the government bailout of the U.S. auto industry has been criticized by Republican lawmakers and proved unpopular with voters.

The Obama administration is eager to cast the GM IPO as a success, but GM executives and government officials have repeatedly denied any political motivation in timing the IPO for the top U.S. automaker so close to the mid-term congressional elections.

Republicans are likely to gain ground when all 435 seats in the U.S. House of Representatives and 37 of the 100 seats in the Senate are up for grabs in the November 2 midterm elections, analysts say.

The high jobless rate is dragging on the Democrats' poll ratings and Republicans might win control of the House and probably pick up seats in the Senate.

The Obama administration has pledged to begin selling down its stake in GM as soon as practical and had said that process would begin in late 2010 at the time GM exited bankruptcy last year.

A final decision on how much of its stake in GM the U.S. Treasury will sell in an IPO will be made in consultations led by Treasury Secretary Timothy Geithner and White House economic adviser Lawrence Summers after the terms of the deal are established, sources have said.

GM is waiting for its S-1 filing to be approved by the U.S. Securities and Exchange Commission.

Its shares will trade on both the New York Stock Exchange and the Toronto Stock Exchange since both the U.S. and Canadian governments helped bail it out.

(Reporting by Clare Baldwin and Soyoung Kim in New York and Kevin Krolicki in Detroit; Editing by Richard Chang)