I forgot about the monorail repairs but you can take the monorail from T2 to T1 and then walk to T3 - we often walk all three terminals to stretch the legs and explore but the bus shuttle shouldn't be an issue.
Also, this says the North line is shuttle bus only so T2F to T3A still has a monorail?
http://www.changiairport.com/content...train-copy.jpg
Im booked for the first time in T2 next year, I usually prefer T1 as its bunker quite but happy to give T2 a try for once.