OK,if Medieval Europeans decided to colonize North America,it won't be as easy in OTL,but they still had technological advances the Native Americans did not. Such as crossbows,siege machines,mills,printing press,steel,steel armor,the wheel,Greek Fire and numerous others. Hell,their castles were perfectly designed for siege andC even the cathedrals could double as fortresses. Plus,they have more livestock which means more pandemics and they have horses. Hell,they have the Black Death and Bubonic Plague which were far worse than Smallpox.
On the Vikings,their longships and navigation;few are their equals in that regard with the exception of the Polynesians and Phoenicians. Their longships are more then capable of a Transatlantic voyage. What probably did Vinland in OTL was the Mini Ice Age which near crippled Europe. So,let's say that there's more reason to go to Vinland and explore. Such as a lot more Norse get outlawed and decide that Vinland is a lot safer than Scandinavia. Either that or they discover the Mississippians and decide to set up trade. Mayhap they discover Maple syrup and offer up honey as an equivalent trade.
One of the Italian city-states like Venice or Genoa decide that the Americas is more economical than the Indies and set up trade colonies,perhaps around the edge of Mesoamerica. Or maybe further up north.
There was tons of persecution against early Protestants,like the Hussites,Lollards,Waldensians,Cathars and any Christian sect that was not Catholic or Orthodox,so mayhap have some flee Europe and set up colonies. Make sure they have provisions,are capable of protecting themselves and that they have a high birthrate,plus are capable of working the land. Maybe that will enable them to survive. Especially if they set up alliances with local tribes.
Anyway,yes Medieval Europeans have the tech,livestock and even germs in their favor. Just won't be as easy as in later times.