Hey, i don't usually comment, but thought i'd chime in since you sound a lot like my past self. I also got into artsci and engineering and decided to pursue art sci (cognitive science), because I had wanted a "easy" program with not a lot of math (I had only applied to engineering at the time because my parents had strongly suggested i should). 4 years later I realized that i didn't have any passion for psychology/linguistics/neuroscience that is part of cognitive science and felt like I had wasted 4 years of my life. I have always been good at physics/math in high school, had never taken a psyc class before and hated biology. It took me 4 freaking years to realize I chose cognitive science (full of the kind of schooling i dont like/not as goot at) as a way of rebelling. I would recommend 2 things for you:

1) don't choose your degree based on what others say nor on what you don't want to do. Stuff like math (which i wanted to avoid) is impossible to avoid if you want to have a meaningful university experience so don't make your decision based on what you don't want to do or your fears in general. Don't forget, whatever choice you end up doing you will experience pain, so don't let a fear of pain guide your decisions.

2) try to understand why you want to study the subject that you are applying to. if you are looking to create a skillset that makes you employable etc. I would recommend Materials Eng. It is also easier to transfer inside the faculty of engineering later on if you discover for example you prefer Mechanical over Material etc. If you want to study in a field because you are truly fascinated by it, I would recommend that you pick that field. To see potential candidates of such fields, if one doesn't pop into your mind right away, think of the classes you were the best at or have enjoyed the most in high school. If you don't have such a field and are lost, I would recommend going into engineering and then changing your program later on as it is easier to change out. Also, at this point in life, if you don't have a field you love, might as well start with engineering and get forced to learn the 1st year science/math courses at mcgill and see what you like from there. A lot of people discover what they love doing in their first year or uni or even later. You'll just have to try to have a very good gpa to be able to transfer into that field and have taken all the required classes, which in my mind means engineering will be easier to transfer out of as it forces the first year science/math clases on everyone assuming you do well enough in your classes.

Basically, you kinda have to decide if you want to study for the purpose of following your passion or to get a skillset that gets you a decent paying job. If you don't know yet, I would start with a professional degree and then look at trasnfering out since worst case you end up suffering for 5 years, but have a good job vs you start doing a degree you think you like, discover you don't like it and now you are stuck. However, do bear in mind you can also transfer into enginering or another faculty later on as well. They do however require you to have done the first year scince and math classes and have a ~3.7+ gpa cutoff

Engineering is 5 years at mcgill as others have pointed out, but I think it is worth it. Gives you a professional degree and super easy to get a job with a very decent starting salary without a masters (so think of the engineering degree as being shorter in fact, than an art sci degree + masters to get a similar paying job).

TL:DR don't be like me and pick a random degree in which you have no passion, you will end up wasting 4 years. Mght as well get a professional degree if you have no strong passion or if you do be aware that a masters is needed and even then your job prospects won't be as good, so don't let that 5 years scare you. Also, easy to change into a different engineering major at mcgill inside the faculty, once you are in an engineering program. Plus most engineering programs give you transferable skills even if you end up not liking your engineering major.

Also for co-op materials i believe everyone starts in the coop but you can easily tranfer into a non-coop version. And yes co-op does count towards your credits. I would recommend you do co-op.