It would depend on if the subjects you wish to repeat are in offered in Summer or Winter sessions. If the subjects are core subjects, you'll obviously have to repeat the subject and pass to be have it count toward your degree. I was looking at subjects offered in Summer and there's not much on offer (though there could be, perhaps in other faculties that I didn't consider).
If they're not offered in Summer or Winter sessions, you'll have to redo them in Autumn or Spring, which will hamper your progress. Any failed subject or subject dropped after census date without an approved withdrawal without academic penalty incurs a fail grade, which will drag down your GPA.