As long as you are either a born Canadian or immigrated to Canada, after your baby is born, you can apply for a citizenship card through a Canadian embassy in the US. See http://www.cic.gc.ca/english/citizenship/proof-eligibility.asp on how to apply. It takes 8-9 months to get the card. Once you have the card, you can apply for a passport for your baby, see http://www.ppt.gc.ca/info/form.aspx?lang=eng®ion=USA
As a dual citizen, your child should ideally have two valid passports and use the Canadian one when going to Canada and the American one when going to the US.
If you were born outside Canada and gained citizenship because one or both of your parents were Canadian at the time of your birth, you can not pass citizenship on to your child. You could however sponsor your child for permanent residency but you would have to prove that you are planning on moving to Canada in order to do that. If you ever do move to Canada, you can apply for citizenship for your child as soon as the child has PR and is living in Canada, that is as long as your child is still a minor when you do that.
