Like he does with "Canto I," Pound decides not to worry too much about unstressed syllables in "Canto II." The only syllables he counts out for each line are the stressed ones, which is a type of meter known as "accentual" meter. Pound would have known that this type of meter is closely associated with old English poetry (we're talking maybe 1100 A.D.), and he isn't afraid to take an ancient Roman poet like Ovid and combine his work with the English tradition. Yeah, Pound knew a thing or two about the history of poetry.
It might be a tricky thing to get your head around, but Old English poetry uses a different kind of meter than the one you're probably used to. Old English poetry only cares about the number of stressed syllables per line, leaving the number of unstressed syllables totally random. Confused yet? Don't sweat it. Let's look at an example:
Aye, I Acoetes, stood there,
and the god stood by me
Water cutting under the keel,
Sea-break from stern forrards (62-65)
As you can probably see, there's no real logic to the syllables that aren't stressed. Pound's also not worried about a predictable rhyme scheme, either. The one consistent thing is that there are three stressed syllables per line, and that's all that matters for accentual meter.
So what's important about this trimeter (tri- = three) pattern? These rules date back to a time when most folks couldn't read or write (or text, even). Instead, they relied on consistent patterns of rhythm to make poems easier to memorize and pass on orally. Pound is definitely borrowing this very old way of putting a poem together. He's sort of like that friend you have with the fascination for vintage fashion. Here, though, Pound is rocking some seriously old style.