Vista said on Monday it would buy DH for C$4.8bn and combine it with Misys, which abandoned plans to list on the London stock market in October 2016, blaming shaky market conditions. Since then, Vista has been considering alternative plans for Misys.

Barclays, Citigroup and Morgan Stanley were financial advisers to Vista on the deal and are leading the debt financing, which is expected to launch for syndication to institutional investors this month, the sources said.

Some US$6bn of debt could include around US$4bn of senior debt financing and around US$2bn of subordinated debt financing, the sources said.

The financing will be mainly denominated in dollars and include some euros and could comprise solely of loans or loans and bonds, the sources said.

Vista was not immediately available to comment.

A US$1.5bn financing for Misys fell away last October after pulling the plug on its floatation.

Prior to that, Misys last tapped the loan market in November 2013, when it raised a US$140m add-on TLB and a €50m TLB. That followed a repricing in August 2013 of its US$16m revolving credit A, a repriced US$84m revolving credit B, a US$921.55m TLB and a €140m TLB.

Formerly Davis + Henderson Corp, DH has transformed itself from a cheque printing company into a provider of payment and lending services. Its customers include banks and credit unions.

DH has close to 8,000 customers, including Canada's five biggest lenders and more than half of the world's 50 largest banks.

(Additional reporting by Hannah Brenton; Editing by Christopher Mangham)

By Claire Ruckin