As of June 1st 2009, Canadians will be required to show a valid passport to get into the United States, whether entering by land, water, or air.

So, if you're driving over the border, you'll need more than just a Photo ID and Birth Certificate or Citizenship card (though bringing them along isn't a terrible idea).

I'd imagine that Passport Canada has learned from their past rush when passports were required to fly into the USA. But I think they will still be swamped. There's only so much extra machinery and resources one would buy to cover a one-time increase in applications.

So I recommend getting your passport renewed or new application sooner rather than later. They've definitely loosened their guarantor requirements over the years to speed things up. Having the get them "rush" or "urgent" will cost you as much as an extra $70, so just get it early. 

Also, if you're an adult in Canada (or you'll be renewing your passport in Canada), you're eligible for E-Pass. Which means you fill out the form online, print it off, and when you go to the office, you get to skip the entire line, saving hours of waiting in a boring room.

Take a look at my E-Pass Canadian Passport experiences here.

I also have maps for Passport Canada Locations in Toronto, Mississauga, Surrey, Montreal and Vancouver.

You can use the E-Pass method for new passports or for Canadian Passport Renewals.