I wouldn't buy the Olympus. It has their 4/3rds type sensor format which is smaller and also unique in DSLRs. It does have some advantages, but there's almost no third-party lens support, and very few used 4/3rds mount lenses available. If you're like me and want to try out lots of different lenses or save some money by having a large selection of used lenses available, Olympus probably wouldn't be the best choice. The Sony would be a lot better, and the Canon even better than that. If you think you might someday want to get a full professional DSLR, get the Canon since a lot of the stuff you buy for the Rebel would work on Canon's most expensive professional bodies too and you wouldn't have to rebuy anything.
Beyond that it's mainly personal, subjective, and touch-n-feel type stuff. Is it comfortable in your hands? Can you reach all of the controls? Are the ergonomics ok? Does the menu system make sense? Is it easy for you to use? For whatever reason my hands always have a ton of trouble with Canon bodies, and their menu system makes little to no sense with me. I like the Nikons a lot better in this respect which is why I'm a Nikon shooter. Other people are the exact opposite. Neither are right or wrong.