I know the pain of going to the wrong major and trying to correct the mistake. I also know the pain of having to wait days & days for someone to post their opinion about your chances (As you can clearly see from my 0 replies thread that I keep checking on). That's why I will try to answer you as best as I can
Getting into masters is easier than Phd's, since you're paying for the education. You can probably get into one of the average schools after completing a good number of courses. However, you want to apply after taking only those 3 courses in the fall?? Furthermore you have listed schools like Berkeley, Toronto, Mcgil etc. These schools are very selective. I'm sorry but there's just no way any of these will accept you in your current condition. I'm just letting you know so you don't waste money on application fees. If you really want a realistic chance, take at least one extra year filled with relevant courses and apply to a whole bunch of safety schools.
I really hope someone more knowledgeable than me can come here and help you.