Hell, just drive up there in your Golf and put it in the trunk. Pray they don't do an inspection when you cross the border. How would they know the difference if you told them that it was your engine that you brought across the border from the states to have a friend of yours look at in Canada, and now you are bringing it back home with you......?
well yeh hey - what are YOU doing in Canada ...
I've meet a few guys at the border (Canadian side) and all I do is write up a bill of sale for a couple hundred and then they drive home. None of them have had any problems. I'd highly recommend not lying to the border people. If I have the VIN number that the motor came from I give them that as well.