Talks, which could result in the world's largest wine business, are said to be at an advanced stage.
The US-based Constellation Brands, worth three times more than Australia's BRL Hardy, which is valued at US$800m (£500m), has denied reports that Blackthorn cider would be axed in favour of its wine portfolio including Stowells of Chelsea.
Simon Russell, PR manager at Matthew Clark, Constellation Brands' UK division, said: "The deal is still an if' rather than a when'. Cider is not a huge profit contributor to Constellation Brands but it is making money. Constellation's strength is operating across all categories. We are not selling our cider business."
Allan Cheesman, Sainsbury's wine consultant and former UK marketing director at BRL Hardy, where he still owns shares, supported a merger.
"There will be cries from some sectors that this would damage consumer choice but I don't agree. Big is fine. It's an inevitability because of the market and it makes eminent sense," he said.
A senior wine buyer at a leading multiple said: "These two would have big money to promote and support products and encourage consumers into the market."