OK, here's a brief statement regarding Officer applications. This is from my perspective, drawing upon my experience as a Res unit Recruiting Officer. I hope this helps a few people.
Resume and Cover-letter:
First off, know the position you are applying for, and do some research on the unit, job qualifications, etcl.
Then, write a proper business cover-letter and resume that highlights your skills and experiences as they relate to the Canadian Forces and the unit and TRADE you are applying. You should also identify why you want to become and officer and why you would make a good officer. You need to think about these things, and then articulate them in writing.
Some units have the option of being choosy. So, like any other businesses, if you just throw together a resume and cover-letter with a few tidbits about how you worked at the arcade or the mall, and not put much thought into it, chances are you won't get that far.
Basically, treat the application to the CF as you would any other business job. It's all about presentation and professionalism.
Reasons for Joining:
There are lots of good reasons for joining the CF.
However, in my experience, unless your dad or grampa was the CO of the unit you are joining, than mentioning that your grampa fought in WWII will have little bearing on your application. In fact, the application is all about you, not what your dad, grampa, uncle, cousin, aunt, or mum did.
Focus on what YOU -- as a person -- can offer the unit and the CF and what the CF will offer you in return.
Interviews:
Again, do some research on the unit and the type of trade you are applying for. For example, if you want to be an Infantry Officer, than do some reading, and find out what Infantry Officers do in the field. Don't come in with a romantic vision of the Officer Corp and talk endlessly about sipping tea with the upper classes and measuring lines of sight with umbrellas. Find out as much as you can about tactics and strategy, job descriptions and responsibilities, and the overall goals of the CF.
Show that you have a real interest in the unit and the military in general.
And, make sure you can talk about it in an interview.