No combination ticket exists for both sides of Niagara Falls.

No.

You have to buy separate passes for the Canadian and US attractions. The border is a real border—different currencies, different operators, different ticket systems. Some tour companies will sell you a package that includes busing you across and a few sights on each side, but that’s not a single admission ticket. If you want to do the Cave of the Winds and the Maid of the Mist and Journey Behind the Falls, you’re buying at least two separate tickets.

Plan on paying twice and crossing the border twice. That’s just how it works.