I did pre-health at George Brown. I found it pretty difficult, but a lot of others found it pretty easy. I struggle in math so that was a big factor, but I pulled through and by some miracle got an acceptance.
Pre-health is good in the sense that it prepares you for the workload you will have in health programs, but other than that there is no reason to pay thousands of dollars for classes that you can upgrade through night school or ILC for free. Especially since there's no guarantee that you will get in, although they make it sound that way. The only reason I went this route was because I thought the college environment would be more motivating, however I am now 4000 dollars more in debt.
George Brown only saved 30 seats out of the entire pre-health program for the rpn. They said you needed a minimum 75 average, but they really mean a 90-95%. I don't know what the seats are like at Seneca though.
I'm sure you've already decided you're going, but just some things to think about!