From IGN's hands-on Mega Man 10 preview:
"Capcom was also quick this morning to strike down the rumor of a new co-op mode in Mega Man 10. Mega and Proto will not be sharing the screen any time soon. According to Capcom, Mega Man 10 is slated to drop in March on all three download services. Expect a $10 price tag."
Amidst the many Mega Man 10 rumors floating about, a postulated cooperative multiplayer mode was undoubtedly the most popular. It's truly unfortunate to see this one ruled out as I'm sure many were hoping this one to be true.
Check out IGN's hands-on preview for more details.