Best way from Niagara Falls to Washington DC
 

I a man going to travel from Niagara Falls to Washington DC with my family with two kids.
Which rout is the fastest and which one is nice and pleasant both nice view?
Which route is toll free?
How much I should pay in toll way one totally?
Which city is beautiful to visit on the way?
Any more suggestions?
Thanks.

How are you getting to Niagara Falls? When is the trip?
Do not try to bring a Canadian rental car into the US.
The toll free route would be US 20 east from Depew to East Avon to get on I- 390 south to I-86 through Bath to get on I-99 (US 15) south through Williamsport PA.
Get off US 15 south onto US 322 to cross the Susquehanna River to get I-81 to get I-83 South on the east side of Harrisburg. I-83 takes you to the beltway around Baltimore and I-95 south to Washington DC.

That is some schlep by car or train.

Why I should not bring Canadian rental car to US?
I will come late July.
Tnx