Are Prenuptial Agreements Legal In Canada

I have a few questions about an international prenup/postnup. I will make a trip to Nigeria Oct.15/17 for a short time and during my stay to visit my fiancée (date for 2 years) we are going to get married. It will be a marriage of justice (something like a justice of the peace in Ontario). I will return to Canada in mid-November of this year, but since my fiancé is a Nigerian, he will stay there until he can come to Canada. He lives there in his parents` house, as usual. A salary there is bad at best, it helps as much as it can at home. His brother in England and I have had to help the family to some extent since his father`s death just over a year ago. I am retired and I receive a monthly pension and I receive a little more. .