Need your suggestion for a business trip to Canada

Dear Friends,

I will need to go to Toronto for a 4-day business trip. Here is my question: I have US green card, and also a Canadian permanent resident card (applied as a family member through my hu*****and). However, I have decided to stay in US, and won't immigrate to Canada. For this trip when I enter Canada, which card should I use - if I use Canadian permanent resident card, they will probably take it back since after landing 2.5 years ago, I've never lived in Canada. If I use my US green card, I guess they can still easily find out from their computer system that I am also the permanent resident of Canada... Well, I just don't want get into any trouble at the airport. Any suggestion? Thanks a lot.