Mom of 2 to american citizen

Hi, i' m new to this forum and have seen so much information concerning american citizen and canadian citizen couples that i decided to take my question public. My boyfriend and i have been together for more than 3 years. we have 2 daughters that were born here in canada. Now we are looking at getting my papers fixed. I used to live in the states with my parents and had a legal status (Permanent resident and a Social Security #) I am cuban and was able to get them quite quickly. Since i moved back to canada with my parents, my residence card expired. I still have the cards in my possession. Now we are looking to get married, but we dont know where to do it (US / Canada) so it can be a much quicker process. Please help us out with our decision. And if someone can inform me on what to do with my expired cards. Thanks in advance !!!!!