Changing illegitimate child's surname into his Stepfather-to-be without his biological father's consent

Hi. I want to know how can we change my aons surname into his Stepfathers surname. I gave birth to him on August 14 2015 and even when I am still pregnant the biological father broke up with me. I am 18 back then and now I am 20 years old. I didnt declare the biological father in the birth certicate, nor guve his surname to my son. Now I met my fiancee a year ago and we want to change my son's surname unto my fiancee's surname. We want to change it even before he goes to Canada and get married? Is it possible? If yes what will we have to do? And if possible can we change it without the biological father's consent?