Birth certificates can be ordered from Ontario.ca. There however you could order only a birth certificate for yourself or your child(ren). If seeking ancestral birth information you should be seeking birth registrations. Certificates are issued by the government based on registrations, cost a fee and require that you provide proof you are the person in question, their parent/guardian, have power of attorney, or can provide proof of death and proof you are next-of-kin.
Registrations are released for public viewing after 92 years and can be obtained worldwide either from Ontario Archives, LDS Family History Centres, or through an Ancestry subscription.