Criminal Inadmissibility

Hi there.
I am from the UK and wish to move to Canada as I have a Canadian girlfriend, and we are looking into the possibility of me being able to live and work in Canada. The problem is that I was convicted of a serious offence when I was 15. I got 3 years for
1)Robbery
2)Possesion of an imitation firearm with intent
Both senteces ran concurrently and I served 19 months, being released when I was 16. I am now 25 years old and have only had two minor charges since then, both before I was 20. So I have not been in trouble for over 5 years. The question is, do I qualify for deemed rehabilitation, and if not what are my options to enter Canada as a permanent resident. Also, seeing the crime was commited when I was a minor, does that change how Canada views the crime?
Thanks in advance for your help