The _______ light and _______ message illuminate if the canopy is not down and locked.

In the T-6B aircraft, the correct response regarding the lights and messages that illuminate when the canopy is not down and locked is indeed that the MASTER WARN light and the CANOPY message will both activate.

The MASTER WARN light serves as a critical alert system indicating that there is an important condition that requires immediate attention from the pilot. When the canopy is not completely closed and locked, it signifies a potential safety issue, particularly during flight operations, and thus, the MASTER WARN light will illuminate to alert the crew.

Simultaneously, the CANOPY message will appear on the multifunction display, providing a clear indication of the specific issue. This dual system of visual alerts ensures that pilots are promptly informed of the condition, allowing them to take necessary corrective actions to secure the canopy.

The focus on both these alerts is vital in ensuring flight safety, as flying with an unsecured canopy can lead to hazardous situations. Other options do not pair the appropriate warning light with the relevant message regarding the canopy condition, making option C the correct answer.