A travel document will be required to bring a baby on a airplane. (I understand from my girlfriend that she has a temporary travel document for her infant not a passport,
but she's crossing the Can/US border she's not boarding a plane.) Here's the site:
Passport Canada: Home
You might register with the Canadian embassy and consulate.
Registration of Canadians Abroad - Consular Affairs Bureau Web site - Department of Foreign Affairs and International Trade
I'm sure Canadians have had babies in DR before, passports get stolen etc. they can process the paper work. But you would have to the proper proof that the baby is indeed yours. Maybe you could email them and find out.
Apply for cancelation insurance for airfare and premium health insurance (if you're eligible with your "pre-existing medical condition")
They have some excellent doctors in the Dominican Republic but how much you would have to pay for a normal delivery and care or a c-section before you go. I'm sure somebody on DR1 knows the answer. Be prepared to pay for hospitalization, change of air tickets etc. and wait for reimbursement from your health insurance.
Personally, I wouldn't do it unless I was sure I had 1st class healthcare lined up for myself and my baby and I could communicate with my physician easily and understand what was going. They have a higher rate of C-sections in the DR. Unless this is your second child, then you can just pop him/her out of oven in a cane field.
Best wishes and lots of joy to you and your husband!