It well known that was no major diplomatic contact between the Seanchan Empire and the nations of the Westerlands before the Corenne; however, I wondered if there was any evidence for direct contact between the two continents at all; via trade and commerce for example?
I answered this in another thread, so I am just going to copy paste the answer here.
I apologize for an incomplete answer, but I only can answer part of this.
The boats that Luthair Paendrag Mondwin was given by his father were specially commissioned to have a vastly different quality than the Sea Folk ships.
I need to go into some deep history I'm only tangentially acquainted with. The Sea Folk were content to stay near shorelines after they first saw the Isle of the Madmen and any who neared those shores were sunk sometime around the Trolloc Wars when the Sea Folk were looking for safer shores. Prior to that there are some sources that the continent of Seanchan was in fact found and there was some small trading, but the female channelers there had been twisted with power and were not deemed safe for their Windfinders to be near. This is how Artur Hawkwing knew there was another continent to send his son to. And that his son would need an army.
Once the armada had crossed the Aryth Ocean, Mondwin knew he was alone and started to conquer Seanchan, which was still very barbaric and had none of the stability that the White Tower had accomplished in the Westlands, small warring tribes and attempts at nations clearly did not have the technology to create ships that would make it across the Aryth.
As to why the Seanchan took so long Mondwhin had insisted that all of Seanchen be captured before they Returned to the Westlands, not wanting to disappoint his fathers legacy. Unfortunately this took a little over a millenia before they were finally able to establish the entire Empire of Seanchan.
To add onto this, no one from the Westlands tried to go west across the Aryth afterwards, simply because they had thought that Mondwhin had perished with his crew and there was no country or person that had the resources to match, or better, the fleet that was sent.
Due to the Sea Folk's complete ignorance of the Seanchan and ease of the Seanchan's conquest of their Isles, it's likely that they were unaware of the Seanchan empire/continent.