Yes, Americans must file tax returns even when living outside of the U.S. There are two ways to do so. You can exclude up to $95,100 of foreign earned income on your tax returns (the new rate for 2012). This means they will not even consider it as income. If all of your income falls into this category then you'd end up with $0 in taxable revenue. http://www.irs.gov/businesses/small/international/article/0,,id=97130,00.html
If you earn over $95,100 a year then you will likely want to take a foreign tax credit for all taxes paid on income to non-U.S. authorities. Unless you earned so little over that you would not owe taxes anyway in the U.S. (or are able to take other deductions/credits that limit or eliminate your tax liability back in the U.S.). The foreign tax credit is meant to eliminate the burden of double taxation. Even if you pay a lower tax rate in your current nation (unlikely in Canada, but anything is possible I suppose) then you will only be taxed at a rate that "makes up the difference" between what you've already paid and what you would have been subject to if the money was earned in the U.S. http://www.irs.gov/businesses/small/international/article/0,,id=97037,00.html
Either way, all Americans must continue to file federal income tax returns.
Finally, if you wish to file jointly with your spouse (as a way to take advantage of certain tax deductions/credits) then they will have to apply for a Foreign Tax ID number. I'm not certain if at that point the combined income would be subject to the $95,100 limit or if it applies individually. I'm not a tax attorney or accountant, just someone who has read up on this a bit.