Canadian MBA GPA calculation: Policy on retaken courses

I'm a student about to enter her third year of undergrad in a genetics program. I realized during my second year that a science degree isn't what I thought it would be and didn't do so well in a couple of courses (It was too late to change programs by the time I realized FYI). As such, I failed a course and will have to retake it during the summer of my third year. I was wondering how MBA's calculate failed courses (ex. taking an average of both attempts, taking the highest attempt, not taking any attempts, etc.). Obviously I'm well aware that this will be a blight on my transcript, especially in B-schools that take last two years of university (Mcmaster , Queens) and cumulative (Ivey, Ottawa). Is there any chance i'll ever be accepted, and what are things I can do to help my application when the time comes. Also, do you think I should take a fifth year to try and boost my GPA and increase course credits so they won't look at my third year summer term? This information isn't readily available so I was wondering if anyone had experienced a similar situation or knows anything about this. Thanks in advance.