
Hi congratulations for your son born in USA.
Because he was born in USA he is a US citizen by birth and he don't need for visa fo entering to Canada with you.
After reaching in Canada you can make a sponsorship application for your dependent son and then the PR application accordingly. You can get all the sponsorship application from the CIC website
http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-how.asp