You don't "report" to customs. When you're crossing back the U.S. guard will ask how long you've been away, did you buy or receive anything, any alcohol or tobacco, etc.. At this point you tell him anything you want ... been away one day, bought some used car parts, etc, etc.. You WAIT for him/her to ask how much you spent and at this point you tell him whatever you want. If you're gonna fudge the number you should decide that ahead of time and even have a bill of sale (doesn't need to be itemized) OR have the seller agree to back you up if they decide to call him (HIGHLY unlikely). If he decides to make you pay he'll direct to the office. Personally I think they'll just tell you to "have a good day" ... as he pulls on the rubber glove 'cause the next car is a Canadian !!!

You'll need a passport to enter Canada as well as return home. You can tell the Canadian customs guy exactly why you're coming to Canada. And you MUST declare anything more than $10,000.. If you don't and they inspect and find it, chances are you're gonna lose it. Other than that, crossing either way is usually trouble-free. Oh, border guards have NO sense of humor so ... don't volunteer any info and just answer the questions they ask.

It doesn't matter which day you travel, its hit and miss.