I see a lot of "Canadian Citizens don't need to fill out an I-94 for such and such visits" in this thread however this is just simply not completely true and misleading. I think if you're not sure of what you're talking about it's best not to answer to such questions and cause confusion.

Certain Canadian Citizens who were born in certain countries (fill in with the usual suspects) need to fill out a new I-94 every single time they enter the U.S. for any purpose including transit, whether or not the previous I-94 expired or not. Failure to surrender the I-94 at departure and/or to follow the exit registration can cause serious problems for re-entry the following times.