I use TD and tangerine, as well as TD investing. I don't keep the minimum balance at TD, but I don't mind paying the fee (which is 3.95 per month, as I have a very basic account.)
The minimum amount you need in there to keep from paying the fee is 1500. If I can get 5 or 6% on 1000 in my cash investment account with TD, then I'd rather keep it there, and it covers the fee cost. I still keep a 500 float in savings, just in case.
Then for my cash buffer, or emergency fund, I keep that in tangerine. It's super easy to use. But I like having a bricks and mortar bank, in case I need foreign currency, or to send a registered cheque, or any other such service. I keep the cash buffer at around 4-5 months expenses, even though it's only earning about 1% in tangerine. Maybe eventually I'll bring that down to 2 or 3 months and invest the rest.