I believe that they are the same. You do not specify which model you are referring to. I understand there are at least three models:
the old adaptall macro 1:2 (1:1 with adapter) 90mm (manual focus) A newer AF 1:1 90mm the newest AF SP IF Di 90mm 1:1 which they say is up to the canon 100mm USM macro in many fields (namely it seems to have a weaker AF system than the canon, which is to be expected, and which shouldn't be a problem, when shooting macro, and other stories you probably already know. otherwise read this http://www.photo.net/equipment/canon/can-tam-macro/ ) the latter is surely available for canon mount and will work on an EOS 300D. I've spent some time thinking on which of them buy. Lately I did the great step and bought the canon (didn't have it yet, I've just ordered it to my local photo shop), why? Because I hate to risk to break the AF system (on the tamron, the focus ring doesn't disengage when in AF position, if you rotate it, god only knows what would happen, well maybe some other persons too;) This was the main reason why. And of course the USM could be handy (this lens will be the only one I have in that focal length range (i.e. >50mm ;), and I'm going to use it also for non-macro work (why not?) canon weakness? the same of all the canon lens line: costs; those fuck**g hoods whithout which your lens is crappy have outrageous prices (45 euros!!!) (which is the same as the first). ciao Danilo.
