Cantor also criticized Gov. Charlie Crist for embracing President Barack Obama's $787 billion stimulus package, vetoing a bill that would have tied teachers' pay to test scores and for even considering running as an independent candidate for Senate.
The Virginia congressman said: "Marco is somebody who has demonstrated he is firm in his principles and his beliefs and he keeps his word."
"We are a nation at a crossroads, and we need responsible leadership in Washington," Cantor said in a statement on Tuesday. "Marco Rubio is just the type of leader our country needs and will make an excellent Senator for the State of Florida."
Crist was considered the heavy favorite a year ago in the Republican primary, but Rubio has risen from obscurity to become a favorite of conservative Republicans.
The Democratic front-runner is U.S. Rep. Kendrick Meek.
The Associated Press contributed to this report.