If you want to immigrate to Canada, look for an immigration class you qualify for here:
http://www.cic.gc.ca/english/immigrate/index.aspIf your occupation is on the most wanted for skilled worker, you can apply for that if you have enough points. You could also try to see if you qualify for the Quebec program. If you have a job offer, you could apply through the skilled worker program if you have enough points or possibly through a provincial nominee program.
If you have a job offer, you could also try to come in on a temporary work permit, see
http://www.cic.gc.ca/english/work/index.asp and apply for permanent residency later.
If you have enough points for skilled worker but not the right occupation and no job offer, you could also apply for a study permit, study for a year and then apply.
After 3 years of living in Canada as a permanent resident, you can apply for citizenship. You would not lose your US citizenship.