If the Norse established a settlement on Markland (perhaps at present day Goose Bay, Labrador) and brought horses with them, the Norse would not be staying exclusively on the coast for very long. The Norse would be traveling inland, looking for furs and probably rather quickly discovering both the St. Lawrence Valley and Haudanasee. On horseback, the Norse could reach in one season, Cahokia and the Mississippian People.
Also, the Norse would not be likely to introduce horses without introducing cattle, sheep, pigs and possibly domesticated reindeer to Markland and Vinland (with all their attendant diseases). Domesticated reindeer to Helulland as well. The Norse got along reasonably well with the Saami to their north. And eventually honeybees for honey for the mead Norse like to drink so much. So yes, we'd be looking at a full blown Ericcsonian Exchange. And Native American peoples would quickly learn the value of all of the Norse's domesticated animals. Sheep for wool, (cows for milk, not so much due to lactose intolerance), cattle and pigs raised for food, cattle and horses pulling plows and all those European crops from wheat and rye to sweet peas and apples and peaches. It is quite possible that the mouldboard plow would diffuse across North America almost as quickly as European diseases.
Then again, there is another real possibility. The local Naskapi (Cree) of Markland would learn the care, feeding and fighting from horses and when the Little Ice Age makes life difficult in the North Woods of Markland, come down upon Haudananasee like so many Mongols and take over eastern North America, all the way to the North American prairie and steppes, growing in numbers and multiplying all the way. Eventually, by the 1400s, perhaps a Mongol style Assaniboine horse empire taking Tenochtitlan and the Valley of Mexico. It will likely be the Cree (Jaffa Cree??

) since the Lakota and the Kiowa and the Shoshoni will likely be overshadowed early on.