This is a big issue
Canada and Mexico will not renegotiate the NAFTA dispute-resolution mechanism, according to a WSJ report that cites people involved in the talks.
This is one of the big issues in talks and a line Canada has said it won't cross. The US wants to be able to opt out of the investor-state dispute settlement and let US courts make judgements. That's a process Canada and Mexico don't trust.
That's a big sticking point but the same report says that "overall, officials and stakeholders briefed say the talks have taken a tentatively promising turn."