My son is currently in Canada on tourist visa, has his work visa approved while in Canada and wants to know how long he has to cross border and stay in USA for. Can he do in same day? He was previously in America on student visa for past 6 months and has now been in Canada for approx 2 months. He has asked me to contact embassy to find out but so confusing
The only requirement is that you leave Canada and re-enter. I did this myself for a Permanent Residence visa and I literally crossed over the Rainbow Bridge to the US, and turned round and came straight back. It's not a problem. (The conversation with the US immigration official was interesting. "What is your purpose in coming to the US? "To leave." "How long do you expect to stay here?" "About five minutes".)
As pnuts pointed out, you will need to qualify for entry to the US for that brief time, but as Australian that shouldn't be a problem.
I think, in retrospect, I didn't even need to enter the US. I just needed to exit Canada.
I lived in Vancouver for a year, and friends/flatmates who had residence permits and visas had to do a similar thing to activate them. They didn't even have to go to the US - they merely 'exited' Canada at the Canadian border in BC, and then entered back in a minute later.
Last time, they literally did it after work. Drove to border, got it stamped etc, came back for dinner.
As a traveller though, I'd at least recommend going into the USA - saves interesting questions later for unusual travel. And why not make a day of it and go see something in the states, is my theory!