I know there -- Niagara Falls and Rocky Mountains in Canada.

is
Niagara Falls中的FALLS是指瀑布,而非复数.there be 句型中的be的单复数要按就近一致原则变换.所以应该是is.
例如:
There is a pen and two books on the desk.
课桌上有一个钢笔和两本书.
There are two books and a pen on the desk.
课桌上有两本书和一个钢笔.