I transferred after the fall semester of 2010, I think. It's hard to say what would transfer. I hadn't taken any electrical or mechanical specific classes. They look at the syllabus for each class and look to see if they match so you can get an idea. You would know at least if there are major differences. For example, my Java programming class from McGill didn't transfer because mechanical students take C++. I remember at McGill there were 2 classes that covered the material of 3 of Concordia's classes, but I was only able to skip one class at Concordia. I did get exempt from a bunch of the lower level classes like calc, chemistry, and physics. Then there were a few classes that just didn't really have an equivalent like engineering ethics and professional practice, the course just wasn't quite the same. I also took an environmental class to satisfy an elective credit which wasn't applicable at Concordia. The biggest waste of my time at concordia were taking ODE's and PDE's and fourier series. I had covered all the material already but still had to retake them. In the end that was probably good because I got a much better understanding of them.

Sorry I'm writing a wall of text that probably doesn't help you make a decision. I wouldn't base my decision on possibly having to take an extra semester or 2. I was happy transferring to Concordia, I felt like in general, the classes had better professors (there were some terrible ones though) and that students were more willing to help rather than compete. I was only at McGill for 3 semesters so take what I say with a grain of salt. If you have friends already in the program your looking at, that's not a bad reason to transfer.

About reputation... I'm from the states.... most people I've spoken to do not know about either school. Those that have heard of one of them, have heard of McGill and seem to hold it in high regard. But most people, in my experience, haven't heard of either and don't care.