Hi, and welcome to the TDP Forums!
Originally Posted by gra2172
I think you need to clarify what you mean by zoom. A zoom lens is one where you can change the focal length - the 17-40mm is a zoom lens, as is your 18-135mm lens. The 'opposite' of a zoom lens is a prime lens, i.e. lens with just one focal length, like the 35mm f/2 or the 85mm f/1.2L II.
What I think you mean when you state 'zoom' (based on "zoom for things like distance photos of kayaks on a river") is telephoto - a long focal length lens. So, it seems you are looking for a 'superzoom' lens - one that goes from wide to long. Lenses like the Canon EF-S 18-200mm, or 3rd party equivalents like the Tamron 18-270mm come to mind. But, their optical quality is not going to be much better (and may be worse) than your current 18-135mm lens. Optically, it's nearly impossible to design a lens to do everything well - compromises must be made. For superzoom lenses, IQ is what you give up for convenience. In fact, that's one of the main reasons for having a dSLR - the fact that you can change lenses and use the right lens for the right purpose.
If you want better optical quality and a broad focal range coverage, I'd suggest a pair of lenses - a good 'walkaround' lens like the EF-S 15-85mm f/3.5-5.6 IS (or the 17-55mm f/2.8 IS) paired with a good telephoto zoom lens such as the EF 70-200mm f/4L (with IS if that fits your budget) or EF 70-300mm f/4-5.6L IS.
A lot of this depends on your budget, so if you can share what you're willing to spend, other recommendations can be made.
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