You need to define the objectives. I have the 18-200mm EF-S IS on the 50D. If you stop down a bit you can get satisfactory sharpness providing you dont't crop more than 25% and you are willing to apply some sharpness in RAW PP (as with the included and updated Canon DPP editor - get updates from the Canon product page for the camera) and unsharp masking in the photo editor of your choice. This lens will not AF on a teleconverter. note that should you ever go to a full frame camera EF-S lenses will not cover the full frame sensor.
This is a very wide zoom range and compromises need to be made. It is a 35mm equivalent of about 28 - 320mm on the 70D crop sensor which has a 1.6 multiplier for effective focal length compared to a full frame camera.
http://www.photozone.de/canon-eos/400-canon_18200_3556is
is one older review based on the Canon 50D 15 MPxl sensor.
http://www.photozone.de/canon-eos is the index of these older review for the 15MPxl crop sensor and shows both EF-S and EF lenses of several manufacturers on this sensor. Your 7D has 18 MPxl. Technical details regarding vignetting and resolution are here in this review:
http://www.photozone.de/canon-eos/400-canon_18200_3556is?start=1
http://www.dpreview.com/lensreviews/canon_18-200_3p5-5p6_is_c16/ is a more recent review here on dpreview with the tech details at:
http://www.dpreview.com/lensreviews/canon_18-200_3p5-5p6_is_c16/page3.asp
At 50mm this lens performs quite well if you can stop down a bit so you may not require a dedicated 50mm.
The Tamron series are also good zooms in general and can be reviewed here and on other sites.
If you need better IQ then you should consider a set of two zooms splitting the range you need between them as suggested in another reply.
Some zooms offer a longer range yet such as 18-270 but that is a very extreme range to get quality across the full range.
http://www.dpreview.com/lensreviews/tamron_18-270_3p5-6p3_vc_n15/ is a review of this lens.
http://www.dpreview.com/lensreviews/tamron_18-270_3p5-6p3_vc_n15/page3.asp is the page of interest here.
Note because of physical structure some lenses will not perform with a TC because of mounting interference. Depending on the aperture you might lose AF speed or it may not work at all.
For my hobby I use the 18-200 keeping in mind DOF and f/stop reduction quality improvements and then after two years acquired a 300mm IS f/4 prime and the TCIII 1.4x. Nature photography is my interest in particular. From my 35mm days I have a Tamron 28-200 zoom that works that I like because it has a focus ring with distance markings. This lets me easily set up a hyperfocal DOF range for night scenes of near field to infinity. I also can use this with my older Lenco extension tubes for macro work. The newer Lenco tubes are made for digital cameras.
You might consider starting with the Canon 18-200 and then later acquiring a 70-200 zoom if you need better IQ in this range or 100-400L EF IS, or a 300 L prime EF IS f/4 plus the TCIII 1.4 (about $2,000 US for the 300 TCII1.4 combo) which gives you a step to high IQ 300mm (480 FF equivalent) 420 with TC (672 FF equivalent) depending on your wallet conditions.
You need to set what kind of venue your goal is to determine your equipment range and quality needs to set up your spending plan.
Another review site is:
http://www.bobatkins.com/photography/reviews/index.html
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Ron Ginsberg
Minneapolis, MN
Land of 10,000 Puddles