Mark Brader:
[1] The onward service to New York -- and the same the other way,
forming the evening train from Niagara Falls to Toronto -- is
subject to significant delays at the border and over the course
of its trip. This also means that if you wanted to go from
Toronto to Niagara Falls, New York, you would be better not to
do it by staying on the train.

Dave Smith:
Almost agreed. Since the OP is staying at a hotel right by the Rainbow
bridge he could walk across to the US and grab a taxi to the train
station.... but he will be getting onto the same train. It may be cheaper
to get it on the US side.

I think you misread either my remarks or Gareth's postings. He isn't
going in the direction of New York City and I wasn't giving advice on
doing so.

The bridge near
the train and bus stations is no longer available to the general
public, but if you want you can walk across via the Rainbow Bridge,
near the falls.

But he won't be crossing that bridge. He will be turning right and walking
upriver.

Not upon arrival, but he might want to see the falls from the US side.
For all I know it might also be convenient for him to board his onward
bus from the US side.
--
Mark Brader, Toronto "1. Buy 64 more buses."
--Michael Wares

My text in this article is in the public domain.