OK, I know there is already another post with questions regarding this but I just got done calling every person and office I can think of and here are the facts that I found.
1st - A DUI or any offense in the U.S. that is also considered an offense in Canada will get you classified as an inadmisable person. They have the right to, and can turn you away on the spot. Below is a link to the general consulate's website explaining this.
2nd - If you do have a DUI AND IT HAS BEEN LONGER THAN 5 YEARS you can apply for what is called an approval of rehabilitation. This is a document that will cost you roughly $200 dollars that must be submitted and approved before you are allowed to enter. There is no guarantee that it will be aproved. If it isn't, you lose the money. Here is a link with more details.
Here is a link to the actual form that needs to be filled out and submitted.
Here is a link outlining all of the documents required when filling out and submitting the request.
3rd (ARD)- I just spoke to a local police officer and our clerk of courts. If you have completed an ARD program you may or may not have the DUI expunged from your record. If your lawyer went through the appropriate process to apply for the expungement then your record should be clear. However, if you chose to not pay your lawyer to take care of it or your lawyer never mentioned it to you then you need to request the expungement yourself. Contact your local clerk of courts to get the details. If you are in Lancaster, there is an ARD expungement PDF on the clerk of courts website you can fill out and submit for $34 dollars.
4th - I have spoken with a few individuals who have recently traveled to Canada with DUIs. All of them said they were asked about it with most of them being allowed to pass. The few that weren't were taken inside and asked to complete the "approval of rehabilitation" there on the spot and pay the $200 dollars. A good friend of mine recently did this and said they interogate you on the DUI more than you can imagine. Eventually they'll approve the request and let you through. However, don't take this as gospel. My source is from a few individuals who were there last year on a bear hunt but I do trust their word.
5th - If you try and lie at all about any convictions you will 99.9% of the time be turned away.
Here are a couple links and sites you may find useful on the matter. Please note that if you call the consulate as I did, they will refer you a lot to their website. Also, the consulates "visa" department does not accept phonecalls of any kind.
Canada consulate - Buffalo NY 1-716-858-9501
Canadian consulate general - NY, NY 1-212-596-1628
Canada border services agency
phone number - 1-204-983-3500 or 1-506-636-5064
Sorry for the new post but I didn't want this getting lost as I spent many days and hours on the phone gathering some of this and wanted to try and keep it all in one spot. You may even want to sticky it based on the hits the other thread got.