Can 3.3V circuit power be used to power garage door opener that uses 3V CR2032 coin battery?
A CR2032 coin cell may start off with a voltage as high as 3.4V - see this datasheet from POWER GLORY BATTERY TECH (HK) CO., LTD. (via Farnell.)



If the garage door opener can withstand a fresh coin cell at up to 3.4V, it should also tolerate a 3.3V supply (provided it really is 3.3V or less.)

If you want more certainty, you could try inspecting the main parts of the garage door opener and determining the ratings of any integrated circuits present.