Kobra wrote:

... do I need a passport?

The requirement for both entry to Canada and return to the US is that
you need to bring proof of your citizenship. That could be a passport,
or, assuming you were born in the US, an original copy of your birth
certificate, with the embossed seal of the issuing agency. A photocopy
is not sufficient.

That said, sometimes they never ask to see it, and if you don't bring
the proper documents, it is up to the immigration officer if he will
accept things like driver's licenses. It's best to bring the right
documents to avoid a hassle.