Research the area and decide what your family personally wants to do and what your budget is. Are you go-go-go from one attraction to the next, are you there for the falls only, are you there for the unique Canadian-ness, etc?
To answer specific questions, yes, with your passports, you can just drive across the border - you will be met by customs going each way at a checkpoint who will check all your IDs and ask some simple questions before sending you on your way.
Where to stay? Having just been, it depends on your hotel standards. The places on the water are MUCH nicer, but can be more expensive...and maybe have high resort and parking fees. To avoid the parking fees, park at the Casino and leave your car and do WeGo for the trip. You'll save money and never worry about where and how to get places (the We Go folks were so good about telling you how to get to places that weren't obvious from the bus stop). We stayed at the Embassy Suites - beautiful, but so busy resort - we avoided the resort fee b/c we booked before it was instituted (it's $25/night for Hilton members, $35/night for non-members) and we avoided the parking fee by parking at the Casino (it's $43/night at the hotel, but the Casino was a flat $5 CDN when we left). I mean, that was $68+tax/night we saved off the top, and that made it very reasonable (especially since we booked on points

...if I had to pay those fees, I'd have been less happy with our stay, but since I didn't, I LOVED our resort

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When to go? You'll want to ride the Hornblower. That is the single must-do attraction. DO NOT SKIP IT

. It does not open til the water is warm enough. This year, that was late (normally it opens late April/early May, but this year, that slipped a few weeks). Also, they do run weekend fireworks after Memorial Day (and then every day after a certain point in June). It's about like minor league fireworks shows, but free fireworks are free fireworks. Plus, in the bridge season We Go buses run more regularly than slow season, but less regularly that high season. So, if I had to pick a date to go, I'd pick when we did this year, the 2nd weekend of June into the weekdays...but anything from Memorial Day til Canadian schools are out at the end of June would probably be perfect (PS - our weather in the June week was absolutely perfect for everything - sun and beautiful walk around weather

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How to pay? Since the US is doing better against the Canadian $, find a card that gives you the best exchange rate (mine gave practically the existing one) and charge everything in Canadian dollars. You will save so much over paying in US $.
I can answer more questions if you have them. Another thing to note - Canadian meals are way more expensive than US ones. Think Disney prices. So, having a hotel which provides breakfast will be a nice thing to both start the day easy and save money

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