I did my bachelor in microbiology, and it was a co-op program, so most of my experiences are lab related ( about 2 years in total)
I also did a part-time internship at my local public health agency for 4 months.
I think I had two very strong LOR, one from a supervisor in a co-op term and the other one from a professor I had in 3 differents classes, so I knew him well.
GPA: I started in another program at first where I got a GPA of 3/4.3 after that I transfered to another university/program where I managed to keep a GPA of 4/4.3 (A). Which means that for my last 3 years I had an A average (was on the dean list)
My letter of intent wasn't really written only for UofT, however I had a very clear explanation of my goals and interests (infectious diseases) and why I decided to switch from microbiology (lab) to public health.
Hope it can help you
Globule