Cirrus is correct, it is certainly possible to see both Tampa and St. Pete from many locations around the bay. But the only place I found where you could see both in one shot (without panning) is from the south end of the Sunshine Skyway near Bradenton:
From that area, St. Pete is 13 miles away and Tampa is 26.
From the causeway to Clearwater, you can clearly see all of the built-up areas of the Bay as well. Here's Tampa, along with its Westshore skyline and the area near the convention center and the McDill peninsula:
Unfortunately my attempt at a pano from that spot did not come out and thus I don't have the angle of St. Pete from there.