Originally Posted by
visualAd
I am also planning on crossing in to the US at Niagara (again with the bike). I have a valid ESTA but would like to know if any additional documentation (except my passport) may be required to enter the US and re-enter Canada a couple of days later.
ESTA is for air and sea travel only. You will need to pay the land border crossing fee ($6 I think) and do fingerprints / customs when entering the US.
I can't actually find an official time limit for how long you can stay in Canada as a visitor... however in the opposite direction, if you entered the US first and took a side trip to Canada, you would not reset the clock when you reentered the US and would only have 90 days from your first entry.