If the ACD period has not expired it could be a problem. I've had clients denied entry to Canada with an open case.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
An open case (i.e. waiting for the ACD to ripen into a dismissal) will cause you entry problems into Canada. A dismissed case, which is what you are stating is your situation, should not. However, you should contact the Canadian authoriites for a definitive answer.
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Canada is a very liberal country where pot is ignored, prostitution is ignored, and the police are polite and honest, but they do not let people with open cases, misdemeanors, or felonies into the country without a Minister's waiver. Retain a good lawyer to get a waiver. It is a $350 application and I have done it regularly for 30 years.