The stability will be different, but probably not greater and lesser.
The one with an arch bottom will allow a little roll, but still tend to keep you people side up. This isn't a bad thing that it will allow a little roll. Why? Well I'll tell you. When it rolls, it will keep a lot of surface area connected to the water. Resistance against the water is what gives you stability. You'll stay in control and be able to get it more straight upright fairly easily.
The one with an all flat bottom will be rock solid steady until it isn't. And when it becomes not rock solid steady, that will be when it loses contact with the water and you are going to go over.
These are called primary stability (the latter one) and secondary stability (the former one). Secondary stability feels more "wobbly" for lack of a better term, but you have the opportunity for better control in more circumstances if you know how to use it. Primary stability feels less "wobbly", but when you start to go over, opportunity for recovery is slight.
In either case, they're both recreational canoes and are going to be pretty high on initial stability. Either one would be suitable for mild water fishing. If you're going to get into bumpy water or swift rivers, you might want to think more seriously about the one with the arched bottom.
- Big D