I'm sorry to rate this so low, but there isn't a great deal of detail in this guide. Most of the "tips" given here are common knowledge among those who have played/played against Duck Hunt Duo in a casual setting and the rest is quite vague. I assume most, if not all people know that Duck Hunts Up-B doesn't have a hitbox.
For the can, you don't have to be standing still to shoot it. You can still move around. You just have to practice travelling and activating it at the same time. It's perfectly doable. It just takes a bit of timing and practice.
As somebody else said, the gunmen have different ranges when firing. Black Hat Mcgee has the farthest range, Squat Sombrero Sam has the shortest. You are correct in sayin' that the furthest range is halfway across the stage.
All in all though, I don't think this guide is indepth enough to warrant its existence. At the moment, this is just a summary of Duck Hunt as a character.