I was a Canadian citizen who was a Permanent Resident in the US for more than 20 years... I only moved back here about a year ago. If you have a Permanent Resident card-- the reflective kind, with the magnetic strip on the back-- you don't need a passport OR an enhanced DL to go into Canada or back into the US. The Permanent Resident card works the same way.
For the record, the hard part is not getting into Canada. The rules are far more relaxed. The hard part is getting back into the US-- but it's no problem if you have a Permanent Resident card.
Any questions, send me a message... I'm an old hand at crossing the border, and living in both countries :) My son was born in the States so actually has dual citizenship!
at 7:31 PM on Apr. 2, 2010