Good evening. I would be happy to help you with this inquiry.
Just so I understand, you are hoping to be hired as a Flight Attendant and Air Canada has previously turned you down for a position and you are uncertain whether your previous impaired driving or over 80 conviction will prevent you from obtaining the requisite Transportation Security Clearance from Transport Canada.
A single conviction for either impaired driving (CC 253(1)(a)) or driving with more than 80 mg of alcohol in your blood (CC 253(1)(b)) should not be cause for you to be denied on your TSC application with Transport Canada if you have valid employment and a sponsoring employer. There are many individuals who work within our airports who have minor criminal records such as this and they have been approved for their TSC.
An offence such as this would not be the category of offence which would see an individual get denied a TSC. Rather, they look at offences such as crimes of violence, dishonesty or drug related crimes. Specifically, any offence which might cause them concern from a security perspective and raise concerns of risk of harm to persons or property.
I expect that your previous rejection was from Air Canada themselves, for one reason or another. It could have been due to the criminal conviction, however it may not have been. Some potential employers will meet with unsuccessful candidates upon request in order to help them understand why they were turned down and what they can do to better their chances in future.
If you had actually been successful in being hired by Air Canada, subject to a successful TSC approval, and you were then denied, then it would show definitively that Transport Canada was causing the issue in denying your application. That does not seem to be the case here.
I would suggest that you keep plugging away and keep focused on your goal. Many of us have dealt with disappointments when applying for jobs and I expect that this is simply the case here. But if you keep applying, and get some feedback if they'll give it, you'll land the job your looking for and you'll find that your conviction won't hinder you from getting your TSC.
Please let me know if you have any further questions or need further info.