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Is difficult to answer, couldn't find the best lens for your 7D because I'm not you, but I could suggest a way for you discover yourself what would be the best:
I think if you aren't exactly sure of what you intend to shoot at this time, any macro lens in the 100mm to 50mm (any brand, most macro lenses today are very sharp) will work to you, I would wait a little more to have the 100mm L is, will explain latter.
With any lens at this focal you could find what macro style fits best your work:
1. You find yourself shooting most of the times with tubes or reversed lenses for high magnification and closer view, the MP-E is the lens for you.
2. If you find yourself struggling for more working distance and compressed backgrounds, the 180mm is the lens you are looking for.
3. If you develop a good work at close-up distances 1:4 to 1:1 without the need of high mag neither more working distance, the 100mm is L is your lens.
4. If you discover the most of the shoots with the macro lens would be infinite focused portraits of people and pets (uncommon in this board but very common in 100mm and 60mm lens groups), trade the lens and get a 85mm or 135mm
5. If the most of the shoots were from home still objects, keep the lens intended for testing the water that should be more than enough for this use.
Edit: Added few more ideas