Honest is the key but there are some important dates you need to know, I will advice you to know them very well before going for the interview.. They are likely to ask you how you met her, year, date.. When both of you sees for the first time, who visited first. Date of your wedding, date of traditional wedding or any other ceremonies. How many guests that attended that day, the first day you met the both parents, siblings, friends and relatives. Where she is working, her position in her place of work, how did she travel to Canada, year and month. Why you didn't travel with her, what do you guys have in common. How much they are paying her per hour, house address and so many more..
You need to answer this question to shows that your wedding is geniue, I don't understand what African guys don't normally have such dates offhand. Study it very well and be honest. Above all pray because that's the only key I know.
Self confidence is very important, eye to eye contact with the interviewer is very important as well. Smile, don't frown your face.. Good luck