Choosing A Scanner

You're always going to see the lighting that way from a scanner, because that's how they work. Both the actual scanning sensor, and the lighting, are on a bar extending across the bed of the scanner. The "scanner" part passes over the coin first, with the lighting always right behind it.

There's nothing wrong with the image you present here. It's known that this is what scanners do, and we learn to filter the odd coloring out when considering the coin. You won't be able to show luster with a scanner (not easily, anyways), and it's an accepted part of posting scans.

The only thing you could do is increase the resolution of the scan; your Canon has the ability to create an accurate scan of that coin which won't fit on your computer screen.