Do you really mean an optical viewfinder, or can it be electronic as well? If you specifically mean an optical one, the only choice is a DSLR. If an electronic viewfinder is okay, you can also look at superzoom cameras such as the Canon SX50 HS and Panasonic FZ200; or compact system cameras such as the Olympus OM-D, Panasonic G5 and Sony NEX-6.
I have an old Canon PowerShot A540, and I would like to upgrade to a newer camera with a stronger optical zoom and more pixels. I am partial to Canon, but not exclusively. However, I absolutely need an optical view finder.
Any suggestion will be appreciated.