Just an update. I actually bought a 2.5 HP mariner 4 stroke. At a very good price. A far better motor than my old dt2 suzuki 2 stroke in every way , except weight. The 4 stroke mariner is smoother, quieter, starts easier and has a neutral gear. A good 20 plus percent more powerful too. And actually planed my sib be it briefly.The useful power you get out of either of them will depend on how well the prop matches the boat.
Either motor can have problems.
If you need to frequently lift the motor off the boat, then the 2 stroke is a plus, due to the weight and less issues with lying it down carefully to avoid the sump oil escaping. The fourstroke might be quieter and use less fuel.
The two stroke might have a better spread of torque so less sensitive to the correct propeller.
You may find that neither is exactly a game changer compared to the existing 2HP.
I would probably choose on condition.
Some of those small 4 strokes have a problem with the neck of the fuel tank being exposed to sunlight and failing if kept outdoors too much, a new tank is expensive.