Welcome to the forum!
Those cameras are quite different actually, Can you tell us why you're thinking of those two in particular?
If you have a Canon digital SLR, then I would recommend the Canon 500n simply because then you can easily share lenses and flashes between them.
If not, then perhaps the Olympus system is a better option at first because the lenses are very good and much cheaper; generally speaking the lens you put on a camera is more important than the actual camera body.
Having said that, the bodies you've mentioned are vastly different - the Canon is a modern typical 90's consumer camera with lots of electronics and automation, while the OM10 is a typical 70's consumer camera, and has far fewer features. It wont stop you from getting good photographs, but try to get the manual adapter for it too, otherwise you wont be able to control both shutter speed and aperture on it.
If you know you need a particular feature, then its much more likely the 500n will have it.
Actually if you are able to get other models, then I'd recommend the Olympus OM20/ Canon EOS 50 (Elan II in the USA I think) as similar but better than the OM10/500n respectively. There are of course
far better film cameras made by both companies - the professional models are very affordable these days. If you're just starting out though, buy a cheaper one that does 80% of the same things and invest the savings on lenses.
Oh and lenses, For Olympus:
a 50mm non-zoom is extremely useful. Fantastic image quality and quite able to shoot in low light. Get the 50mm f1.4 if you can afford it, if not a 50mm f1.8 is still great. From there try "doubling up" - a 24mm (wide angle), a 100mm, and 200mm if you'd like to capture more distant things. Vivitar make some pretty decent 70-210mm zoom lenses too.
For Canon -
a 50mm f1.8 is still extremely useful . Other than that i think zoom lenses are your best option, taking into account price vs performance vs practicality. I only know about the wide angle zooms because thats whats most useful to me - Canon 20-35mm f3.5 and the Tokina 19-35mm are comparable; a Canon 22-55mm f4 is also there is cost is the overriding factor.
Hopefully this was in some way useful
