Mattsack2,
You need to speak to the Canadian Consulate and ask for a waiver. I have heard that it costs about $300. If you go to the U.S. State Department website there is more info on how to contact the Canadian Embassy.
You are not the only one who has had this happen. If you had done more research which you apparently didn't, you would know that if the DUI question is asked on a detainment, you can get turned away at the discretion of Canadian border authorities. There is a warning about this on the US State Department website. I have been asked about DUI convictions MANY times, but unlike you I am not a law breaker.
The Canadians don't want American DUI convicts driving around on their roads and killing their citizens. It's very bad politically when that happens. It makes them look like they aren't enforcing the laws. And it is a problem, although primarily with young Americans in the 18-21 age group who can't legally consume alcohol in NY or Vermont, but can do so in Canada. In case you did not see it, it was also the cover story on TIME magazine this week so it's not any secret that DUIs are epidemic in the USA.
I work in the US legal system and I was recently in a very busy criminal docket in a courthouse in Connecticut which was fucking swollen with DUI cases. If you ask me, penalties for DUI must not be stiff enough because people keep doing it. We have a 1 free pass law in Connecticut where on first offense you go into an alcohol education program, unless of course you kill someone or seriously injure them in which case you can go to jail. However there are too many repeat offenders. People need to understand you can't drink and drive. I was nearly killed yesterday in a head on collision by a guy who had to be drunk based on the way he was driving. I avoided the collision in part because I drive an expensive German car which handles like no other when you need to make a sudden turn.
For these reasons, I feel as though the law is fair and the Canadians appropriately denied you entry. You are a law breaker and you have no entitlement to go to Canada. In fact, if you pay for your waiver and the Canadians let you in, consider yourself lucky because I personally feel the waiver is bogus. Think of it as an insurance payment that you won't drink and drive and kill someone in Canada. Maybe you have learned your lesson and if so, I wish you well. But your post evinces an attitude that you did nothing wrong. You in fact did do something wrong, and you are now paying the piper. In fact if you only drank and drive once as you say, and there were no personal injuries or property damage inflicted, how did you end up with a conviction? I think you are not telling us everything.
By the ways, I do agree with you about the hypocrisy of Canada letting in the terrorist types who are all over Montreal, but denying you entry. But the truth is, you are a more imminent danger on the roads. The terrorist types in Montreal are probably only planning attacks against the USA and are no immediate threat to the safety of the average Canadian like voyageur11.