It's pretty hard to compare uni marks to school marks, and uni marks vary greatly from course to course - at my uni, for example, it's much easier in some sense to get an 80 for a science subject than a law subject, because the law subjects are marked according to a bell-curve that only allows 2-5% of students to get 80+, whereas science subjects are not.
In general, however, I'd say getting 70+ is quite doable for an intelligent student, but certainly not easy. If you got As in that subject at school, then if you put in the required amount of work, you ought to be able to get 70+ in that subject at uni. If you got A+s, then likewise 80+. But this estimate by no means is particularly accurate; I've had friends who "only" got 89 for their ENTER but average well over 80 at uni, and similarly friends who got 99 but get low 60s (in law, admittedly).
So it definitely won't be easy and you'll very much have to be focussed on making sure that you get your desired marks, but it's certainly doable.