Get a US CBP decal online.
Register with EAPIS.
Get the OSH NOTAM (it's out). Doesn't change much from year to year, but get this year's anyways. Basically, you don't talk, and you don't squawk. Get in line at the correct place and altitude, and do what you are told. Enthusiastic wing-rock to ack ATC.
Get USA VFR Sectionals and some kind of airport directory (I use AOPA).
Plan a route - probably through the Sault. I go direct over Lake Michigan, you probably don't want to do that.
To actually cross the border, you will need do EAPIS, and file - and activate! - a flight plan. And to enter the US, the FAA NOTAM says you must have a squawk code from ATC. If you do not have a transponder, fly a formation and only the leader squawks ALT. Be sure to remember to close your flight plan!
You will need to choose an airport for your first landing in the USA, to clear customs. There is a list here:
http://www.cbp.gov/xp/cgov/toolbox/contacts/ports/
Arrive at OSH with plenty of fuel in case you have to orbit. Stop at Appleton for gas, for example. No side by side, no under and over. Have a beer at Friar Tucks and shower at the red barn.
Bring US cash, comfortable shoes, a hat, sunscreen and tiedowns. Put a blue tarp over the wing to keep the water off, and put your tent underneath it.
On the way back, call 888-CAN-PASS to let customs know you are coming. 2 hrs notice is required. You need to choose an airport. File a flight plan - and AUTO-OPEN - with 800-WX-BRIEF and be sure to file an EAPIS departure. Close your flight plan!
Hope this helps, and thanks for the help you gave Eric!