You won't get a lens to cover Macro, landscape and wildlife in one go. If you want a longer reach try to locate a Sigma 50-500mm F4-6.3 also called a bigma but you need bright conditions to use it at longest length. Don't think the Sigma 70-200mm F2.8 is well regarded by users and is not in the same frame as Canon's 70-200mm F2.8. I use the Nikon 70-200mm F2.8 VR with both 1.4 and a 2x converters, handheld in most conditions without problems. I've also used the Sigma 50-500mm F4-6.3 with a Sigma 1.4 converter, but manual focus only, with good results at 700mm but you do need bright conditions. You could also consider the Canon EF 70-200mm f4L USM at under £500 and use a converter/extender with it to get the extra reach.
