Visiting from VISA-exempt country Mexico (complicated situation)

Hey Guys!

Ok so I'll try to make it as brief as possible; My family and I applied as convention refuges to Canada over two years ago, I was not the main applicant, my dad was (I'm only 19, was 17 at that time) the application got rejected, we applied for humanitarian and compassionate grounds and it was rejected as well, we decided to leave Canada shortly after that so we didn't get deported (May 2008); however my girlfriend is there and since she can't come and visit me then I have decided that I will go and visit her, possibly marry while being there since we both want to make our lives in Canada.

Long Story short, I'll be taking a plane from Mexico City directly to Toronto, I have a letter from my school stating that I study there and I will possibly get a letter from my employer here saying that I have permission to be absent from work for a week, this is considered to be a "vacation" and I don't have a problem pretending I'm a tourist, the thing is, I don't think I want to disclose any of my past to the Immigration officer because it will definitely raise doubts and I can't afford to be denied entry.

1.- I will also be buying a round-trip ticket and making a reservation for three nights at a hostel, will this information be enough?
2.- Do they have access to all my previous records? I obviously won't mention anything unless otherwise asked, but I plan to stay with the "I'm a tourist" part
3.- I have a brand new passport since the older one with the Canadian stamp had expired, do they ask you if you have ever visited Canada before?
4.-Any recommendations?

Thanks a lot for the support and comments guys!