Hi there,
I'm not sure about the other questions you have since I'm new to all this and I don't want to give you a wrong answer
But I'm curious about the 5th one and I have 2 questions:
1 - why do you consider this as an admission withdraw? You needed to leave Canada to go through the Canadian border and validate your Canadian visa and that's it. It is like you went to the USA but stayed only for a couple of minutes instead of couple of days.
2 - You have to mention in the DS260 all times you went to USA, do you think you need to include the flagpole as well? I did the flagpole but I didn't put in the DS260. Reading your question made me think I probably need to include it because in theory I went to the USA even though I stayed there for 10 minutes only
1 - I have a stamp on my passport that clearly says that, I think that if it's on the passport it will be registered somewhere else too, I ticked YES in the question "have you ever been refused entry in the US..." and explained everything.
2 - Yes I did mentioned all the times I went to USA, but doing Flagpole basically denies entry to the US in order to turn around and go back to the Canadian side. So I did write that experience in the question mentioned above, hope I'm doing it right..