Although it has been years since we have camped along the Niagara area, there always were lots of excellent campgrounds. We have never been hassled about bring normal groceries across the border. However, at times of disease outbreaks, such as mad cow, potato blight, hoof & mouth, etc you might find "local restrictions" going either way, but nothing like US restrictions for when you want to come back, for example you cannot return with any citrus even if you can prove that you brought it with you when you crossed. We face restrictions on alcohol & tobacco, so you should check as to how much you are allowed.
As Ruth said, no hand guns of any description (you won't need them) and long guns by prior arranged permit only for hunting trips. It isn't worth the risk of getting caught trying to bring them in illegally.
Firewood is a truly local issue, but many locations will not allow any from outside their area, be it Canadian or outside the country. Forestry remains big business, and there are many examples of non native species getting a foothold and decimating a section of the industry. However, I doubt that you would run into difficulty in the Niagara area, since it is primarily agriculture and tourist, little forest.
While set up, take the approximate 1 hour drive into Toronto, which offers much to see and do. There are a lot of excellent wineries and wine tours in the area, and Niagara on the Lake, is a beautiful town, with lots of shoppes and an excellent live Theater, if interested you might want to check it out and pre-book tickets.
Enjoy your trip.
Ed
And lastly, don't get too upset when you discover that most people do not end every sentence with an "EH", or that you won't get push and poked while waiting in line to see the attractions. BTW, the overall best view of the falls is along the fence at the start of the Horseshoe Falls.
