Which is better: 3kW Hub motor or 2kW mid drive motor.
I don't see any pedals on that photograph, so I don't see using a standard mid-drive motor.
So, you are asking about a motor mounted where the petrol motor is and driving the rear wheel with a chain, or replacing the rear wheel with a motor.
Driving by chain means gear reduction is possible so a motor may spin faster and/or deliver greater torque. You might also switch to a Gates Carbon Belt drive.
Direct drive means no chain at all, and more room for a battery lower in the frame.
The weight of a hub motor will have significant effects on the response of the rear suspension if it's much different than the current hub assembly. It won't have much effect on the passenger weight - just the rear suspension response.
After this, you are into questions about desired RPM from the rear wheel (required - this is critical, what do you calculate?). Total expected weight. Desired range. Length of any significant hill you may need to climb.
You may not get complete information from any motor seller, but that won't stop you from calculating what you need, because you need what you need, based on what you want to attain. Ask for help about specifics.
Engineering means answering all of the questions, and then finding the sweet spot where they all overlap. Let us know.