My wife and our son and his family, three little ones and spouse are visiting Niagra Falls in two weeks.
You might want to check availability as they tend to book up well in advance so cost might be a driver. Here's a link to Insider reviews of US and International Marriott Properties. You may find this helpful. Marriott Insider's Hotel Review Master List
As a family the best Marriott is the Courtyard on Victoria. Book the package that gives you dinner voucher of 40 dollars and free breakfast at the Keg restaurant or TGIF. There is a frequent shuttle to the falls and it is a short walk to all the kid touristy stuff on Clifton Hill. The Courtyard has biggish rooms and can handle 3 kids.
The two Marriott hotels on Fallsview are spectacular for adults, with a great view of the falls from falls facing rooms. A few downsides of there for a family is the add ons. Destination fee of 12 bucks or so and a parking fee approaching 50 bucks. The restaurants in that area are very expensive with the chains imposing a 1.5 times up charge on their menus compared to down the street.
Check out Groupon or WagJag for deals. Especially going in the off season you may be able to get a deep discount on things.
Remember you are in Canada. You need all the paperwork to get here. Especially for the kids. Change your money before you go at your bank. You will get a much better rate than if you use USD at a vendor. There is likely a 2.5% currency exchange fee on your card, unless you have the marriott one, so cash is gold. Also do not expect American Express to be widely accepted.
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