Parking prices in the Fallsview area are driven by demand. Slack days at the casino can be as low as $5. Busy days can be far higher, even up to $40.
I have never paid to park whenever I have stayed at any of the hotels in this area. Traditionally, getting the free Players Advantage Club (PAC) loyalty card and letting $20 cycle through a slot machine was enough to get free parking in the large casino parking garage. A new operator took over a couple of months ago so I am not sure what the current standard is. If you are unloading a group at the Embassy Suites just tell the parking attendants that you are not parking with them and that you will move once checked in. They will ask for your keys so they can move your vehicle out of the way of others as required, but they will not have a problem with it. They all know that it is far cheaper to park at the casino. If you don't have much luggage just park at the casino outright and walk over.
When you are in the casino you can ask at the PAC desk or check your online account to make sure that you have earned free parking.