It depends on the situation, usually all new immigrants are given a visa in one go. Due to thier backlog they may not be able to issue your baby a visa in time for yours to expire, so they may ask you and all accompanying members to undergo medicals again with the baby (as your meds will expire in a years time). If you inform them about the probability to give birth in your home country they may not even the issue the visas to you now.
Regarding your second question, unfortunately it is not totally unheard off and a lot of people have done this. However as you are supposed to inform CIC immediately about changes in your family composition (births, deaths, etc.) till the time you have landed, this may pose as a challenge for you later, as CIC rules stipulate that any child wether accompanying or not must under go a medical exam before your landing, or else you may not be able to sponsor them in the future: http://www.cic.gc.ca/english/information/applications/guides/5196ETOC.asp
However I have no further information on how people have beat this system, maybe some of the other members can help, if you post this question on one of the topics that are more frequently visited. I would advise speaking to a proper immigration lawyer to confirm if you can sponsor the baby later. In my opinion the delay in getting your baby's visa before you can travel, will seem worth it, when you will have to go through the sponsorship headache later.
Regards,