Yes. Without delving into the semantic problems with using the word "discovered"(as if the people living there didn't count) the exploration and (brief) colonization of Greenland and Newfoundland by Viking explorers is well-accepted among historians.

And then, of course, there's that Gavriel Menzies fellow...

It absolutely is. We have both literary and archaeological evidence of Icelandic settlement in North America from the 11th century in the form of Vínland saga (the earliest extant manuscripts of which date from the 13th century) and the L'Anse aux Meadows site in Newfoundland.

Aside from the Norse around 1000 CE, there is no evidence of Afro-Eurasian contact with the Americas, or vice versa. There's really "less than zero" evidence, since we would expect such contact to leave some sort of archaeological, linguistic, biological, or other such evidence, and yet our evidence for the Americas militates against such a thing, with independent growth and development.

I wrote a longer post on this subject a couple months ago, specifically looking at claims of paleolithic European migration (i.e., the Solutrean Hypothesis) and afrocentrist claims of contact, but also linking to earlier discussions of claims of Native Americans being lost Israelites; Brendan the Navigator; Gavin Menzies' nonsense; and a little bit about possible early Basques.

The obvious "yes" answer has been given. One point that needs to be made, however, is that in spite of the arrival of Norsemen to Canada, the the existence of North and South America did not as a result become common knowledge in Europe, Asia, or Africa.

EDIT: Changed a bit from original comment for clarification.

I thought it was known that English and French fishermen had come as far as the Canadian coast prior to Columbus? Not settled but been here, stayed to load up on fish then went back.