Thank you for your question.
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Yes this may very well be a serious issue.
Because of your criminal record at first you are considered to be inadmissible to Canada on the basis of criminality.
But, after 5 years has passed since your sentence as been completed it is sometimes possible to be deemed to have been rehabilitated when you reach the border. However, there's no guarantee as it's up to the discretion of the immigration
If you don't want to take a chance at the border the most prudent thing to do is to apply for individual rehabilitation. If this application is successful you will no longer have to be concerned about being turned away at the border.
But, it takes over a year to get this processed.
So, if you want to come up before then it's sometimes possible to get what is called a Temporary Resident Permit (TRP). This is really your only option at this point in time. It may work though there is certainly no guarantee.
Here is a link to the information about the TRP application: http://www.cic.gc.ca/english/information/inadmissibility/permits.asp
Here is the link to the webpage that explains how rehabilitation works:
Let me know if you need any further clarification.