Scansion is the pattern of a poem’s meter – its repeated pattern of feet – stressed, unstressed, etc. While this feature played an important part in poems of earlier periods (Romantic odes, or Shakespearean sonnets, for example), cummings is trying for a different effect, not a repetition but a unique pace and rhythm closer to actual spoken phrases than to musical rhythms. Our “normal” way of talking breaks ideas into phrases by breath control – for example, “they sowed their isn’t they reaped their same” would in regular conversation, have a breathed pause after “isn’t (where a comma would appear in normative written prose).
When an “informed reader” (q.v.) says this poem aloud, he or she will automatically follow these unwritten conventions. What cummings has done by not indicating such breaks with punctuation is to give the reader the same “construction” freedom as the unconventional grammar (“they said their nevers”); the poem therefore becomes a “creation” of the reader as much as a piece of prescribed writing by cummings.
Now, having established this goal in cummings’ poem, there are some “metrical feet” – notably iambics and trochees – simply because they are built into the English language (“autumn winter spring summer”) – but the “payoff” for breaking the poem down into feet is elusive at best, and counteraesthetic at worst. As one hears when cummings reads the poem himself (http://www.youtube.com/watch?v=DTuClB9Xh6w), a “natural”, slow recitation gives the poem all the “meaning” it needs. The temptation to apply “poetic terms” from more traditional times to this poem (and this applies to the rhyme scheme as well – rhymed couplets in some stanzas but not in all) is like looking for a streetmap in a Mondrian painting.