To be honest, I was in the same position you're in, during my grade 12 year. I had a brutal high school physics teacher, and physics is my weakness. But, as long as you have 6 courses that have higher marks than physics, those marks are what will determine your average to get into university. Since physics isn't a required course for lifesci entrance, it won't be counted in the top 6. Just take your required courses and some easy electives and you'll be fine.
You'll end up taking physics in first year lifesci anyway, and if you don't take highschool gr. 12 physics, you'll have to take
two physics courses instead of just one, which will definetly impact your
GPA. I'd say take it in highschool where it won't affect your average too much, and you'll (hopefully) only have to take the one physics in first year life sci.
this is the reasoning I came up when I had to make this decision last year
Good luck!