What is an I-94 Border Pass?
An I-94 card is the proof that you have undergone a criminal record search in the U.S. (conducted by the U.S. Department of Immigration and naturalization). If you're record is clean, on criminal record on file, the the INS will issues the the I-94 card. It's nothing more than proof that you've be checked and verified clean.
As a matter of good operating practice, every Canadian driver with no criminal record should apply for an I-94 card at their earliest convenience, especially in light of Sept. 11. Showing the card to U.S. Customs and Immigration inspectors will speed up the process at the border.
It's a different matter if you have a criminal record. You can apply for a waiver, and if you're accepted, you'll be issued an I-194 card. That tells INS inspectors that you do have a record, but that you've been granted a waiver and been given permission to enter the U.S.