As a peek into what what you might be up against, check out "squidgate"
by Peter Watts, a sci-fi writer that questioned a guard as he was leaving
the US back into his native Canada. He got arrested and convicted of a felony for not getting into his car fast enough and asking why they needed to search a car that was leaving the US. He's a real nice guy and might even offer some advice if you contact him...
Also here's a link to an audio of Customs harassing and arresting a couple going shopping in Niagara...horrible stuff.