Laser camera focusing aid on white surface

Hi everyone,
I'm a newbie in the laser world. I started to discover this technology yesterday after having problems focusing with my camera (5d MK III + Canon 100mm macro 2.8 IS) on a white surface with almost no contrast.
Infact the lack of contrast makes the focusing very hard or at least it takes many seconds until you point to a more contrasted part!

To solve this issue I'm thinking to attach a laser to the flash shoe of the camera so that it creates some kind of pattern (maybe just a dot is fine).
The problem is that I don't really know what kind and strength of laser I would need for this purpose.

I will be pointing this white surface from less than 30 meters away (probably it will be actually less than 10 meters) and it would be really nice if the laser is visible with sunshine on the white surface.

Any suggestions?
Also, any idea of some accessory to put it on the flash shoe and since I need it as fast as possible where to buy it in Belgium or a really fast shipping website?

THANKS A LOT!

It will be difficult for an AF to work with. Light always confuses my DSLR. That said if you use MF, it could be of some use. Try searching for laser cat toys that have the lenses that make the dot a shape. Those will be easier to make sure are focused. No idea as far as using the mounting bracket though. Low power though. Higher powers make the light bloom. Also you may have issues with glare off of the white surface as the light will be slightly reflected.