It was my understadning that you do need passports, but if you are already getting them then it's a mute point.
We live close enough that we drove. I think we actually stayed at that marriott the first time we went just hubby and I and i remember liking it.
There is a little tram you can ride to get from one part of the falls to the other, can't remember if there was a cost. that might have been part of Goats island??
The falls are neat but honestly I get bored if i stand there and watch them for more than 10 mins lol
We enjoyed the maid of the mist and got soaked but it was fun.
we did not go behind the falls i don't think but i would like to.
There is a ripley's believe it or not museum in the town but i think you would need to drive to get there. which i found creepy and tiny but your boys might like it.
other than checking to see if they have a night time light show or fireworks.
and maybe doing dinner in the revolving resturant, i think that's about it. some sounvenior shops.
Personally unless your 3 days include travel time, or just chilling relaxing at the hotel you could probably easily see everything in 2 days only.
I'm hoping someone else chimes in since my memory is bad, but that was my impression about 3 yrs ago.