The discussions could result in more than one cornerstone investor being brought on board and are for each investor to take a 150 million to 300 million euro ($171.21-$342.42 million) stake, these sources told Reuters, declining to be named as talks were confidential.
Cornerstone investors are institutions that are invited to subscribe to shares ahead of an IPO to boost its popularity and often serve as a seal of approval for other investors. Securing such investors is popular among Nordic companies.
Första AP-fonden (AP1) had been asked about being anchor investors, its head of equities Olof Jonasson confirmed to Reuters, but declined to comment on stake size and price.
"We have been approached but I couldn't really tell you anything about the details... Our interest... would be about business potential and valuation and all those things put together," said Jonasson, whose fund is also a large owner of Swedish rival AB Volvo.
Reuters reported last week that VW expects to sell shares worth 5 billion-6 billion euros ($5.7-$6.9 billion) in an April listing that could value Traton about 20 billion-25 billion euros.
At this size and value, the IPO could potentially become Germany's and Sweden's biggest new share offering in 2019, but the sources said its size had not yet been finalised and would depend on market conditions.
AP4 head of equities Per Colleen said he could not confirm any of the details but added: "Anything of that size, we will have a serious look at".
AMF, Investor AB, Folksam, Volkswagen and Traton did not immediately respond to requests for comment.
Traton is the umbrella name for MAN, Scania and VW brands, but Swedish company Scania is by far its most valuable part, with superior profitability and stability.
Scania was listed in Stockholm until 2014, when its then largest investor VW took it private in a deal that valued it at about 17.9 billion euros, but many Swedish investors that were squeezed out said then that the offer undervalued the group.
One of the source said that Swedish funds were keen for a substantial stake in the Traton IPO as they expected it to have a large influence on the automotive and engineering-heavy Stockholm blue-chip index that they try to outperform.
($1 = 0.8761 euros)
(Reporting by Esha Vaish in Stockholm, additional reporting by Alexander Huebner and Edward Taylor; Editing by Rachel Armstrong and Emelia Sithole-Matarise)
By Esha Vaish