Just to give a little more insight..
When I was 18 I wanted to join the Marines, my mom is a U.S. citizen and I filed for a greencard. The red tape is long and thick, the waiting times are very long, and keep in mind the sponsor must live in the United States while they are sponsoring you for a greencard. It turned out I was a U.S. citizen because my mom lived there for over 10 years. Then another expensive process began to prove the time she spent living there, I still need an immigration lawyer to finish the process but I'm not even thinking about paying the lawyer costs or moving there until I'm done university. Comparing the cost of university here in Canada versus the U.S. and how little the Marine Corps reserve pays compared the Canadian Army reserve I made the right choice going to school here.
I'm not trying to be harsh, but as someone who is familiar with the process, I can assure you that there is NO WAY you can join the U.S. military, period. It doesn't sound like your parents are U.S. citizens either, so you can forget about a family sponsored greencard, or any other type of greencard. I'm not trying to force you to join the CF I agree it's not for everyone and may not be what you are looking for, but you need to find something else to do with your life, trust me, don't waste another day thinking this is a realistic option.
If you have any more questions, you can private message me. It's better you find out this is impossible now before you put your life on hold on or embarass yourself telling everyone you are going to join.
-Steve