Supposing rhymes with:
juxtaposing, opposing, proposing, composing, decomposing, disposing, exposing, imposing, juxtaposing, opposing, overexposing, posing, predisposing, proposing, reimposing
Supposing sounds like:
savaging, sobocinski, spacing, spasms, speaking, specimens, spicing, spiking, subconscious, sufficiency, suffusing, suspicions