" Would we be able to cross with a weeks worth of groceries ect on board without much hassle? " It should not be a problem, reasonable amounts for personal use. There are not the restrictions entering Canada as there are for entering USA. Large quantities of alcohol and tobacco products could be questioned. Passports (passport cards) simplify the entry to Canada and are required for re-entry to the US.
When we stay at the Lundys Lane KOA, there are lots of American licence plates in the park, can't be too many problems crossing the border.
The city shuttle bus, available at campground entrance, to the Falls area, and
Niagara Parks Wego transit eliminate the need to find street parking or expensive $$$ parking lots at the different attractions.
Beverley and Ken