The Calgary-based company says it's offering Suncor shares worth about $4.3 billion and would take on about $2.3 billion of debt owed by Canadian Oil Sands, making the total transaction worth $6.6 billion. Suncor says the offer would give shareholders of Canadian Oil Sands a stake in Canada's largest integrated energy company, which includes the Petro-Canada chain of fuel stations as well as its own oil and gas production and refining operations.