A few good sites for Canadian immigrating to the USA are
http://www.visajourney.com/forums/ and a new one is
http://www.familybasedimmigration.com/forum/index.php
The marriage based Visas are the K3, or the Cr-1 or Ir-1. Cr-1 is married for less than 2 yrs, and the IR-1 is married for more than 2yrs.
If your USA spouse is a permanent resident of canada, then you can Directly file (DCF) at the closest USA consulate in canada. Then you would be applying for either the cr-1 or IR-1. DCF is usually the fastest marriage based visa. If the USA spouse is not a permanent resident of Canada,then one ahs to go the regular cr-1 (ir-1) or K3 route, which can take up to a year! Lots of info on Visajourney.com, just look under K3 or CR-1/IR-1 forums. Each of those forums have "stickies" that explain on how to file. Or you can hire an immigration attorney, but beware, many are clueless and not cheap! We had 1, based out of New York and cost us $2500, plus filing fees. Wish we had found visa journey, everything u need is there, even examples of filled out forums, etc etc, and its free to ask questions. One just needs to sit down and read the stickies at the top of each forum, (K3, Cr-1) I do belive one would require a Cdn mailing address.
Another route but not certain is for the CDN to stay in the USA and adjust of status (AOS) but if you went that route, the CDN could not leave the USA until the AOS was complete. I'm sure others will post and give u assistance. But give VisaJourney.com a look, as wel as the other 1 I mentioned. Cheers