The Canadian province of British Columbia, between the metropolis of Vancouver and its vast mountain forests and oceans nearby, has become the third-largest film production center in North America thanks partly to tax incentives, and its ability to stand in for the Pacific Northwest (usually Seattle or Portland) or any small, rural town in the northern half of the US. You could describe the city as "one giant backlot, a bunch of anonymous buildings that can stand in for anywhere else."
Another Canadian city, Toronto, has doubled for cities such as New York City and Chicago more times than it has actually represented itself.
Montreal has usually played Francophone cities like Paris as well as American cities like Boston, St. Louis, and (again) New York City.
Utah has been Vulcan, Mars, and most famously the Old West.
Georgia and Louisiana have represented not just the Old South, but also modern Midwestern suburbia, northern industrial cities, and the jungles of Africa and South America.
New Mexico has represented New Old West settings, modern Southwestern cities, midwestern suburbia, and the Middle East.
North Carolina also is known for this trope - the larger cities like Charlotte and Raleigh have portrayed Midwestern and East Coast cities while Wilmington and the surrounding Cape Fear region has stood in for almost everything under the sun.
Australia is also a place that does this - Brisbane and Sydney have played various American cities, the grassier rural areas of New South Wales and Queensland have doubled for the English countryside, and the Aussie outback is often used as a stunt double for locales such as the Middle East, various alien planets, and the desert parts of California.
New Zealand has been used as a stand-in for, among other places, Japan and New York State.
South Africa's varied natural and cultural landscape and multi-racial population has allowed cities such as Johannesburg and Cape Town to double for small and big U.S. cities and various European cities, and other locales there to play everything from the American Deep South to alien planets.
In Europe, filmmakers of the '70s and '80s working on a low budget loved to film in Spain or Italy. This was a major factor in the rise of the Spaghetti Western genre, as the deserts of Spain and the easy availability of Spanish-speaking actors made filming your Mexican-set westerns easy.
In the 2000s and '10s, Eastern Europe became popular with action and horror film producers working on a budget, with liberalising governments offering nice tax incentives for foreign film productions and plenty of actors who can play vaguely-Russian sounding bad guys.
