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BeShoo said:
You can drive across the border and then come back, or if you tell the U.S. border guards that you're landing, they will give you a piece of paper in the office sending you back.

If you want to get an appointment in an office in less than two months, you need to tell them it's urgent and they will try to accommodate you, but going to the border is much simpler and much faster if you're anywhere near there.

Just don't make the mistake I made and arrive past 11:30 at night when all the immigration people had gone home. That didn't work. :)
I tought they work 24/7 :o
 
Some do, some don't. http://www.cbsa-asfc.gc.ca/do-rb/menu-eng.html
 
DanSlh said:
I tought they work 24/7 :o
I thought they did, too, but the immigration people at the particular crossing we went to (Prescott) don't work all night. Checking canuck_in_uk's link, the immigration people at that crossing are off at midnight, but the primary inspection guy said they go home at 11:30. We got there about 11:35. He said that if they were in the middle of dealing with another traveller at quitting time and we were next, we would be out of luck. Had I checked that link, we could have gone to the Thousand Islands crossing which we drove right by a short time later.

The reason we went to Prescott is that we were already extremely close to it and we thought we'd be clever and avoid paying the bridge toll by using the turn-around lane before we got to the bridge. The agent asked if we'd been in the U.S. and I told him that we just drove around the building. He told us that you can't do it like that. You have to go see U.S. Customs and Immigration first. We also wanted to make a quick shopping trip to a U.S. Walmart, but it was getting late. We did get to Walmart in Niagara Falls a couple of days later instead.
 
Well, ours came today! Unfortunately, it seems like we've misplaced the CSQ, so that's another headache.