Honestly alternate history where they bring back tobacco.

Potatoes didn't really spread outside of South America until colonists showed up. East Coast (were Viking activity was found) settlers and by extension local indigenous peoples actually first got their potatoes from Ireland, which then spread through the US.

Corn is still a possibility, the main issues that come to mind being that it actually needs a large population or gets inbreeding depression very fast (genetic bottlenecks are a huge issue with European heirloom corns) and the whole nixtamal thing. Using ash and lye is a thing in some traditional European foods, maybe the conditions in the early 1000s would have allowed the practice to be taken back with the corn and prevent pellagra deaths that happen when un-nixtamaled corn becomes one's main source of food.

Edit: actually I'm double checking my corn sources and 1000ish AD is kinda pushing it for when corn made it that far north and east.

Oh I was definitely thinking of the brief chaos between maize becoming popular and Europeans figuring out nixtamalization.

Maize is also pretty picky about where it'll grow well so you'd probably have to put most of it down in Italy, southern France, Spain, that sort of region. The Vikings definitely can't do anything with maize back home.

I'm always annoyed that the thing about China going to America in the 1400s is unhinged pseudoscience by a guy who thinks Atlantis was real because the funniest alternate history imo is Lewis and Clark crossing the country and arriving in Oregon or whatever to find a burgeoning Chinese colony.