Hello,Well, you don't need a US visa or flag pole. A flagpole is a letter which is like refusal to entry in USA. So you will return back to Canada and enter again in Canadian border.
I went to 1000 island Canada Border Service. ( Thousand Islands Bridge). It just took 15 minute. I am done with my Landing . It was a great experience . People are good and they are operating 24 hours a day and 7 days a week (means you can also go on weekend).
Pedestrians: I asked patrol officer that can we cross it on bridge. He told we do not have pedestrian walk way but, yes, they do accept if someone come with flagpole letter from across border. (It was a confusing answer but I think it is not a busy place and you can use road side walk to cross border). Is it you are not sure or have any confusion, then call Canada Border Service customer care number and ask them they can help you with this. (ask customer care to connect to Thousand Islands Bridge office or ask them to call and solve your query)
Have a good day and BEST OF LUCK.