I'm in Canada and I went to school a long time ago but fwiw at that time it was easier to transfer from Engineering into Science and not lose time/credits while those transferring from Science into Engineering basically started over. I believe this was due to the fact that engineering had very few elective courses (I think I had 3 in 4 years) and so many courses had prerequisites while sciences had more flexibility and people that I knew were able to count the engineering course as an elective for example. Obviously ymmv but it might be something to research if he is still on the fence between those two worlds when it comes time to apply.
Universities up here each run their engineering programs differently. My first 2 years were generic engineering and then 3rd and 4th you picked your specialty (it was changed to 1.5 years after I went through). Other schools have you apply directly to a specific program for first year. Even at those schools much of first year is common so it is often possible to switch specialties (DH did this years ago and a friend's kid just did it last year). Some specialties have more overlap than others though.
This is still the case in most Engineering programs I know. Easier to drop "out" of Engineering into math/science programs that get in. And it depends on the program but many school still do a generic engineering for two years and then you choose a specialty. Depends on school.
As to my DS he doesn't KNOW if he wants Engineering at all. I just think it's would be a reasonable fit and would like him to explore while in H.S. He is in the Robotics Club at school. And it's OK if he is on the fence when he goes to apply for schools because he could apply to some Engineering programs and some not and delay the decision. But if he decides he isn't interested in it at all it would be useful to learn sooner than later. Particularly as to do well in an Engineering program you need a bit of passion for it.
Just looked the local "Open House" will be when DS is out of town. But I could think about sending to the Bay Area Maker Fair this spring with his grandfather. My parents would probably even happily buy him the plane ticket.
