Trade was something I didn't like in Rome. This is handled better in EUIV.
The this province exchanges this resource with this province model was simplistic, tended to structure internal markets and was a state managed top down model that would be more true of the Palatial Bronze Age than the more complicated Iron Age / Classical Age.
Apart from certain state managed enterprises that had a specific purpose, the primary example being ensuring Rome's grain supply, which applies only late in the period covered by Rome, trade was largely left to entrepreneurs. The state's interest was in extracting taxes from economic activity.
So similar to EUIV please, but probably without state directed merchants. Unless perhaps you have state officials with specific duties, like ensuring Rome's grain supply ?
Yeah, provincial trade was really annoying, although I liked how strategic ressources were important. Not having iron, horses or wood was really a strong incentive in trying to get those. Though once you had one, having more really lost its appeal. In EU, what you have, or don't does not really matter.