I don't know canon macro lenses but you have to realize that all macro lenses will achieve the same magnification of the object. That is, if you are photographing something 1cm big an proper macro lens with 1:1 reproduction ratio will mean that 1cm object is project into a 1 cm area of the sensor. Thus it will take up the same area of the frame. (as an aside, this is why smaller sensor cameras can do very well with macro).
The difference between a 50mm macro and a 200mm macro is merely how close you have to be to get that 1:1 ratio. the longer the focal length the further away you can be, which is great when photographing an insect that might get scared. However, it gets very hard to photograph a long macro lens.
So I think a 50mm macro will do just fine, even wider can work for product photography on a crop camera. Aperture is irrelevant because you are going to need to stop down.
Some things you will want in addition to the lens for product photography:
* Tripod and decent head. You don't want to be hand holding macro stuff
* MAcro focising rails. Fousing is a bitch at macro work. You want to manually focus, and since DOf is so small then moving the camera closer or further works bets. You can do this with special rails where you can mechanically move the camera closer/further millimeters at a time. Moreover, due to the tiny DoF of macro work you may want to be doing stacked photographs and fusing them together. E.g. you have 1 photos with the front in focus, move the camera forwards 2-3mm and get another photo with the next layer in focus, and repeat that dozens of times. There is free software to do the fancy stacking to it take the sharp inffocus portion of each photo.
* There are special flashes for macro that provide more even light in close proximity.
* General lighting and lightbox. You can build this yourself with a big cardboard box and white card. Get some powerful white lamps from Wicks shining in both sides through a diffuse (like thin paper).
* remote release. Once the camera is set up on the tripod you don't want tyo be touching it due to the focus issues and the fact that tiny vibrations are magnified. You can use the camera's timer with 20 second delay but a remote release is going to be. faster. You want the mirror locked up and a 3 second shutter delay .
