This is an excerpt from Sonnet 18 written by Shakespeare. If you know anything about Shakespeare's sonnets, you know that they always have a regular meter, which means that all of them are written in iambic pentameter. This means that the first syllable is unstressed, and it is followed by a stressed syllable.
So, when applied to this poem, just split the words into syllables - the first one will be unstressed (so, as, can, or, can), and the second one will be stressed (long, men, breathe, eyes, see).
(I took the penultimate line as an example)