My interview took 25minutes at most - the  officer asked questions based on what I put on my application - so just be truthful and you do not need to worry about the interview - also make sure  you have all your originals as she asked to see the originals -  I applied for caregiver  - so she asked me a few first aid questions- what if a child drinks something under the sink with no lable on it-  what if the child chokes and the parent are out of town -  common sense questions-
the other thing is why do I think  Canada will be a good country for me to work in? 
I was not prepared for this one but I just had to think fast and cooked up a few things like - healthcare- also I read about Canada being the most peacful country in the  world -  was voted by UN- the officer was impressed with this  - she had read the same story online - so hey go for it - it is worthy it!- good luck to everyone and always put God first he will lead the way for you!