[Cdncarnut]

Have a passport.
Leave any handgun at home.
Take off your sunglasses, turn off the radio and put your vehicle in park.
Be clear about where you are going and what you are going to do.
Make sure that you tell then that race as a hobby and not a business.
Also, if they ask, be sure to tell them that there is no money to be won. You are racing for a trophy and bragging rights.
If you luck out and depending on where you cross, one of the Canadian Border Guards is a fellow racer.