I hope you realize that you will have NO aperture adjustments. It will be a fixed aperture only, probably something like f11 (which is not very good) and the only way to set exposure is by changing the camera shutter speed or ISO.
Camera shake at that aperture and that magnification is a huge problem, which means to get non blurry images even on a sunny day you are setting the ISO to a minimum of 800 and more likely 1600. Images in low light are virtually impossible.
For zoo work, this setup is IMO completely impractical. Not only is it a huge setup to carry around, but everyone who sees you is going to ask if you are on assignment for National Geographic (I am not joking, even though anyone remotely familiar with the magazine should know they do not use zoo shots). The zoo staff, depending on the facility, may also question your motives. The only people who really use these as far as I know are wild bird photographers and if that is a major interest of yours it might be worthwhile. But for zoos forget it, just buy a telephoto lens.
I am not trying to be negative, I am trying to save you from plunking down money for something that will not be a real solution. If you want advice on good telephoto lenses for Canon, try a photography forum or you can send me a PM (I am a Canon user and photo instructor at a pro photo lab).