Lamontagne rhymes with:
buntain, contain, fontaine, fountaine, lafountain, lafountaine, maintain, abstain, aquitaine, ascertain, attain, brattain, buntain, butane, chastain, contain, costain, detain, entertain, fontaine, fountaine, lafountain, lafountaine, maintain, mustain, obtain, partain, pertain, petain, retain, sartain, stain, sustain, uptain
Lamontagne sounds like:
landesman, landsman, linthicum