I'm not an immigration lawyer, but I am a visa officer for a private company (I make sure the companies clients and staff are visa compliant and apply and maintain their visas correctly). As a rule any offence that shows up on your record (and in some same cases not even these) will make you inadmissible to Canada. The onus is on the applicant to prove otherwise. The CIC is not equipped at all to discern what is a crime in one country and how it corresponds to criminal code in Canada. DUI is often cited on CIC forums and websites because it is one of the most common crimes in the world. In Canada a DUI is a hybrid offence, hence why even police officers who commit this act can sometimes keep their jobs after completing sentence. Dangerous driving and driving with a suspended licence fall under this category, especially if the fine has not been paid.
Personally, I have seen everything from shop lifting, filing for bankruptcy in the past, drunk and disorderly, disturbing the peace, and even admitting to a crime but never actually been formerly charged or convicted (A Client at a Canadian point of entry had correspondence on his phone about smoking pot with friends while in Thailand, and had to wait 5 years from the dates mentioned in the e-mail to apply for rehabilitation). Now not all these people were refused legitimately and had different options to appeal the decision (depending on the visa being applied for). However, this process is long, expensive, and in many cases requires good cross border legal advice. As most of these cases involve nuanced legal codes from multiple countries, lawyers are needed. Again, lawyers are expensive, and usually not within the means of the average person, especially a young couple applying for spousal sponsorship. It also means the CIC creates collateral damage as the Canadian sponsor will most likely leave Canada in a form of de-facto exile to be with their loved one. This serves no one.
Overall, Canada is one of the harshest countries in the world when it comes to admissibility, and it has not been proved statistically to protect Canadians in any way. In fact, crimes committed by foreign entrants has not changed from the old days when people used to stroll into Canada with a driver's licence. We call this "security theatre" in the business; Look like you're protecting Canadians even though these policies do little. Ultimately, it only hurts Canadian citizens. Citizens wishing to bring their family to Canada, the Canadian tax payer who has to pay for all this unnecessary bureaucracy and Canadian investment and tourism. Furthermore, CIC and CBSA will tell you this is not a punishment but a precautionary act. However this is clearly not true, as real dangerous criminals who want to get into Canada, generally don't try through PR applications that take years, they would just illegally cross.
The only thing I could advise, is try and wipe this from your record (although I realize most US states have no pardon system), however failing this, get your sponsor to write to their local MP to get some sort of action or review taken on your case. This is a bit of a long shot, but I have seen it done before and it is always worth a try. It also draws attention to the issue as this affects a multitude of Canadians. Also, if you are close to the Canadian border, some points of entry can process rehabilitation applications in a matter of days, and they may be able to work out your case and you can talk to a real human being who will decide your case (Contact CBSA to find out). Inadmissibility is a very serious international consequence of serious crime, but unfortunately Canada and the CIC use it as a dragnet to make their jobs amiable.
