Yes, you can enter the US with a DUI in most cases. A DUI is a criminal offence in Canada. It carries with it many serious consequences, including a criminal record, even after you have fulfilled any obligations such as paying fines or serving jail time.
However, it is unlikely that a DUI conviction will prevent you from entering the US unless there are multiple offences or there are additional charges. If you have ever been denied entry, you would need a US Entry Waiver.
A US Entry Waiver is provided by the Department of Homeland Security. Issued for a period of one, two or five years, it holds more authority than the staff at the borders. Even if you have a criminal record, with a waiver, you should be able to go to the US.
When you try to go to the US, you may be required to disclose any items on your criminal record. If you were convicted of a DUI under the Criminal Code of Canada, you would have to disclose this. However, they will usually allow you to enter with a DUI, so stay calm and be truthful about it.