Which Taxes Do I Do?
There seems to be some confusion with regards to taxes. It's actually very simple. If you work in the U.S, and come back to Canada within two years, you owe Canada the money you didn't pay to the IRS. For example, if with your salary you would have paid $20 000 in taxes to Revenue Canada, but the IRS only took $10 000, Canada would ask for the other $10 000 if you move back within two years.
When it's time to do taxes, you have to do your taxes for both countries. There's lots of tax accountants that can file for both countries, and it can get complicated if you were married and one spouse lived in the other country for awhile and you file joint returns. With the Canadian tax return, you only have to file for the part of the year that you worked in Canada. That is, you'll only have to do it once.
Canadian Residency Status
It's possible that Canada may ask for some taxes if they consider you a "resident." Having a valid license might even mean being a resident. That's why it's important to cut ties as much as possible. The legal arguement in my opinion is taxes pay for the services rendered by a Government. You pay taxes so your Government can build you highways, manage the economy, etc... So why should you pay taxes for services you're not using and unable to use.