I don't think you're going to find a true macro zoom lens, that is to say, one which will yield an image on the film the same size as the object. Many zooms say "macro zoom," but they in my experience give 1 to 4 or 1 to 3 at the most. Also macro lenses typically are optimized for high resolution and aren't very fast - say f2.8 at the fastest - unless you pay REALLY BIG BUCKS! I can't speak to Canon, but Pentax has an excellent 50 mm and also a 100 mm. I'd suggest a 100 mm since it gives you better working distance from bugs, etc, and less likelihood of casting a shadow on the subject.
100 mm on a 35 camera also makes a pretty good portrait lens, in addition to being a short tele. I scored a Vivitar f3.5 100 mm macro some years ago which is/was inexpensive and very serviceable, despite being a "plastic fantastic." It goes to 1 to 2 from infinity, and then from that to 1 to 1`with a dedicated achromatic closeup lens. If you find one, be sure the closeup lens is furnished. These are also marked under the Cosina name, and probably others. I'm sure they are in Canon mount, although which Canon mount I don't know. There is an autofocus edition, but for macro use I have never felt the need for autofocus.
You could consider closeup lenses for your present lens. They are available in various powers, and need no exposure change, as tubes do. They may well degrade the image quality some, its your call on whether or not that is objectionable. They are the cheapest route.
Extension tubes are another way to go. They fit between the lens and the camera body, and thus enable very close focusing. Be sure to get tubes that will maintain automation with your camera! Tubes do require extra exposure, but with TTL metering this is automatically done.
Note that if you have a lot of extension, and stop down for depth of field you may encounter exposures of many seconds. Then reciprocity failure can rear its ugly head. That is a topic for another discussion!
I've tried extension tubes with a zoom lens, I'm sure it can be done, but I'd rather use my macro lens!
If you intend to do macro or close to macro, save money out for a decent tripod, and a focus rail would be nice. Makes positioning the camera so much easier. Get a cable release. Unless you have an interchangeable viewfinder on your camera, a right angle finder sure beats lying prone on the ground looking through the finder!