Canon does make a 28-300 mm f/3.5-5.6 "L" lens, but you have to
sacrifice image quality and aperture.
The 70-200 mm f/4L IS or f/2.8L IS II (note the mark II) would be my pick. They're the sharpest of the 70-200s and IS works very, very well - e.g. I can take reasonably sharp photos at 1/8 sec, 200 mm.
I've owned/used the 85L, 100L macro, 135L, and 200 f/2L lenses extensively, and the 70-200 f/2.8L IS II compares favourably to all of them at f/4 or smaller. The zoom is very good at f/2.8 too, but the vignetting is somewhat intense (a bit like the 17-40 at f/4).