Freedom of expression is a Charter right, and protects you ONLY from government interference with expression. It does not give you a freestanding right to say whatever you want about anyone with impunity.
Two sides of this: Contract law and defamation law.
Defamation Law: If you defame somebody, then they can sue you for it. If it can be established that you made the statement, and that the statement is defamatory, then the onus falls to you to lead an affirmative defence. Truth is one such defence. If you can prove, on a balance of probabilities, that what you said is true, then that would be a defence. But the thing to remember is that the onus is on you: If you can't establish the truth of what you're saying, you're toast.
Contract Law: Whether or not your agreement precludes you from reposting the reviews...well, it depends on the language. If they were the least bit well-drafted, they would. In which case the dealership is entitled to demand that you remove them, and could sue you for monetary damages and potentially equitable relief forcing you to take it down. ***It would not even matter if the statements were true.*** The fact that you agreed to retract them could be enforceable and binding.
find an attorney specializing in personal injury.
lawyer fees are part of the "damages incurred" where i come from, never paid a cent to my lawyer directly and they are not taking a percentage either.