I believe it is an American estate, because of the flags, but I don't know where.
This is the former Round Island House / Hotel Frontenac / The New Frontenac (with annex building) on Round Island near Clayton, NY, United States. The New Frontenac existed from ca 1898 till 1911, when it burned down. For pics and more details on its history, see Clayton's Historic Island Hotels by Rex Ennis.
Some more pics of the former "New Frontenac":
Here's a map showing Round Island with the "New Frontenac":