Experiences will vary depending on your high school and your work habits, but in my experience EngSci was no harder than high school. In fact, I think my marks in EngSci were higher than they were in my last year of high school. I left EngSci after the first year, however, because I found that my interests were in math and not at all in things like design, chemistry, electronics, biology, etc. Anyways, the point is that there isn't really any telling how tough it will be until you're actually there, no matter how many people tell you it will be tough. To be safe, however, you ought to be prepared for the worst.
The program offers a good variety of courses, especially in first year, and you'll probably enjoy that. Try to network with a few people; if you're living on residence, especially one that's close to Bahen and where all the EngSci lectures are held, it should be easy. That way, if you miss a lecture (or all of them ;)) or you need answers to something, you're not on your own. I found that most of what you needed to know for most courses was right in the textbooks. When I was there, all the courses had something of a homepage on an internet database called CCNet. These course websites were very useful. Often they would tell you when the upcoming quizzes/tests were, what to study for them. Sometimes the assignments would be on these websites. These pages also have message boards and when I was there, they were very active so all the EngScis were able to communicate with each other and clarify things for each other.
When you have labs, you might not do so well on the first one. Figure out what your lab supervisor expects of you, and then make sure you really do that on your subsequent reports. If you do 3 pages of error analysis and he wants more error analysis, do more! When it comes to exams, some of the nearby copy places (places where you go to make photocopies and stuff) sell packages of past exams. These packages might also be available through the EngSci department. Get these packages and do them. They are great preparation, and you might even find questions on your exams that are identical to those on previous exams.
By the way, you probably won't have your electronics course until second semester, but if they're asking you to use "Electrical Fundamentals" by Zukotynski and Kherani, Third Edition then I can sell you mine.