MLB is not, at this point, considering canceling the 2020 MLB season, per multiple reports. Scott Miller says that the owners had their weekly phone call today, and the subject of canceling the season did not come up.
The Miami Marlins having multiple players test positive, resulting in the team staying in Philadelphia (where they played yesterday), has led to the cancellation of their scheduled game tonight in Miami against the Baltimore Orioles. The Orioles are returning the Baltimore, so clearly there will not be a game played in Miami tomorrow, either.
In addition, the Philadelphia Phillies, who played the Marlins yesterday, are all being tested, and their game against the New York Yankees this evening has been cancelled.