The Thais have laboured in the final group round for qualification for the 2018 World Cup.
Goals from Sarawut Masuk (33'), Theerathon Bunmathan (65') Siroch Chatthong (76') and Chanathip Songkrasin (83') -- known in Thailand as 'Messi J' -- destroyed the visitor's slim chances of overturning a two-goal first-leg deficit.
The emphatic win, 6-0 on aggregate, installs the War Elephants as favourites against Indonesia when the two sides meet next week.
Title-holders Thailand dispatched their cup final opponents 4-2 in the group stage.
The Thais have laboured in the final group round for qualification for the 2018 World Cup, but have sprung to life playing against their Southeast Asian rivals.
On Thursday a rout appeared on the cards after Thailand took the lead through Sarawut, who met a delicious cross from the left with a diving header to make it 3-0 on aggragate.
That left Myanmar with a mountain to climb and inevitably gaps appeared as they stoically hunted a goal.
The pick of the goals came with around 15 minutes to play from the War Elephants' rangy striker Siroch, who celebrated his birthday by thrashing the ball home from an acute angle after latching onto a neat long pass.
His side will play Indonesia in the two-legged final on December 14 and 17 after the Garudas edged passed Vietnam 4-3 on aggragate on Wednesday.
Thailand, who have won all of their Suzuki Cup games so far, will go into the final brimming with confidence and with the group game win against Indonesia under their belt, a result led by a hat-trick by star striker Teerasil Dangda.