The Americans can deny you entry to the US if you have a criminal record. If you have been fingerprinted by the police and later convicted for a fraud, theft, drugs, or any other conviction, then the US border agents can see your fingerprints and conviction on their screen and deny you entry to the US.
If you decide to apply for Nexus, you will need to make sure you do not have any criminal offence as your application will be rejected and you may be subject to requiring a US Entry Waiver, I-194 and I-192. Many people have made the mistake of applying for a Nexus application only to find out it is rejected due to a past criminal offence or even a criminal charge that was later withdrawn, dismissed, stayed or discharged.
Once we obtain a pardon, record suspension or file destruction then you will be safe to apply for Nexus as long as you have never been stopped by the Americans in the past.
If you have been denied entry to the US, then you will require a US Entry Waiver or I-194 and I-192 to return to the US. A US Entry Waiver is a complicated process that costs money and takes time but it is attainable.
Here is a recent communication we received from Nexus about their character assessment when approving the application:
The Canada Border Services Agency (CBSA) is conducting a public consultation regarding proposed amendments to Regulations under the Customs Act governing Trusted Traveller Programs (TTPs). The amendments will clarify the eligibility criteria that will replace the good character provision, the conditions of the authorizations, and the circumstances leading to suspension and cancellation of membership.
The CBSA website provides detailed information on the changes, as well as the rationale behind them.
As a valued stakeholder, you can provide your feedback on these changes by replying to this email no later than 11:59 p.m. (EDT) on August 19, 2016.
Program and Policy Management Division
Traveller Programs Directorate
Canada Border Services Agency