I was wondering if it was possible to use lenses on cameras made by two different companies, like Cannon and Olympus.
What is AFIAK
As Far I as Know, (or As Far as I Know, mixed up)
There are a few exceptions, but in general you can't. Sony bought Konica/Minolta, I think, so you can use Konica-mount lenses on Sony cameras.
Sure there is, as long as you don't mind doing everything manually.
On eBay go to the Camera & Photo section and type in mount adapters, just checked and it came up with 396 items.
20D and a couple bits of glass.