Junior Internship

I'm a rising junior and ideally I want to get a SA position in IBD next summer, but with the current market and my 3.5 gpa at a semi-target I feel like this will be very difficult. As a backup, I'm planning to stay a 5th year at school if I don't get a banking internship, because getting a FT offer will be difficult without a summer internship, and get my CPA and start in accounting (TAS) and hopefully move to IBD from there. My question is this, do big 4 typically give internships to students in their 3rd year of a 5 year program or are they treated as a sophomore? Also, what would be some other suggestions for a junior year internship that could leave me with the possibility of getting an IBD or S&T offer FT after senior year(assuming I can't get an SA gig at one of those places as a junior)?