Without all the details it is difficult to know your situation and many of us are in the USA so things may be a little different in Canada. Consider these facts from your posts:
$27.5K Out the door cost
$10K Down Payment
4.99% interest rate
This calculates to $281.75/month for 72 months (
http://www.cars.com/go/advice/financ....jsp?mode=full)
So back to your question...."Can I still negotiate the price of the car?"
It will depend on the terms of the contract you signed and the laws where you live. Your worst case is you overpay for the car or give up your $1K deposit. Your best case is you negotiate a better price or get your $1K back.
Regarding the car price.
WHERE I LIVE, The $27.5K price would be far too high. The value of that car in USD is more like $23K out the door.
Finally, never forget that you are buying a car, not a loan, not an interest rate, but a car. Never get deceived by looking for someone willing to give you a monthly payment number that makes you happy because you are then guaranteed to overpay. Good Luck.