FRANKFURT, April 13 (Reuters) - Private-equity held Italian packaging firm Guala Closures is preparing a stock market listing or sale that may value the company at more than 1 billion euros ($1.06 billion) including debt, sources close to the matter said.

Guala's main shareholder, Apriori Capital Partners, will at the end of this month interview investment banks vying for a role in the potential initial public offering or outright sale, the sources added.

The company specialises in closures, such as bottle tops, for sealing spirits and counts makers such as Diageo, Pernod Ricard, Remy Cointreau, Fortune Brands, Brown-Forman and UB Group as its customers.

It is expected to post earnings before interest, tax, depreciation and amortization of up to 110 million euros this year and its owners, which also include the company's management and fund Nb Reinassance, are hoping to reap a valuation of up to 11-12 times that, the sources said.

That would represent a premium to peers such as Polyone , Sealed Air, Berry, Bemis and Ball.

Other packaging groups such as Germany's Kloeckner Pentaplast are looking to the United States as a listing location as most of its peers are listed there.

Guala, which sells more than 14 billion closures each year, will also be marketed to potential trade or private equity buyers, though it has rebuffed offers from groups such as private equity firm KKR on price in the past, the sources added.

Guala Closures is directly owned by GLC Holdings whose main investor is Apriori Capital.

Credit Suisse, which led Guala's 510 million euro bond sale in November, is expected to take a leading role in the potential IPO or sale, which could take place after the summer, the sources said.

Guala, which has 4000 employees, was delisted from the stock exchange in 2008. In the first nine months of 2016, it posted an EBITDA of 74.5 million euros on revenues of 369 million euros. Full year figures are due April 27.

Apriori Capital, KKR and Credit Suisse declined to comment or were not immediately available for comment. ($1 = 0.9407 euros) (Reporting by Arno Schuetze, additional reporting by Stephen Jewkes in Milan; Editing by Toby Davis)