From the acclaimed translator Kersti Juva came out last year a book with the title Löytöretki suomeen (my trans.: A discovery expedition to Finnish), where she tells what choices she has made while translating from English to Finnish (see the linked Wikipedia article for her selected works). In that book she gives several examples how the English "can" has completely different meanings requiring different translations. I can imagine that neither "may" is unambiguous. So we end up having "cans", "mays" etc. on one side and voida, kyetä, pystyä (and several others) on the other side, and there is no one-to-one correspondence between those. For that reason this exercise void of any context is completely useless.
Those infinitives don’t exist in English. “Can” and “may” exist only as auxiliary verbs that don’t conjugate. They’re the same in every person, singular and plural.
To the extent that there’s a “to can” infinitive, it means preserving foods by putting them in cans, eg, “today I am going to can some tomatoes”.
It has to be with another verb to mean "voida".
If you want the translation to be an infinitive verb then to be able is the only option. However, this still needs to be paired with another verb in English or else it will mean "olla pystyvä". As for may/can being auxiliaries, it doesn't make much sense to require a grammatic equivalent when Finnish doesn't have one. So I would not say may/can are wrong exactly... but maybe this exercise is a little awkward.
If voida is an infinitive (which it is) the English translation must be 'to . . .' . There is no such verb as 'to may' in modern English, but like 'can', 'shall', 'will', 'must' etc. it is used with the infinitive minus 'to' of a verb to indicate modification of the meaning. In Old English 'to may' meant 'to have power, to be able', but in the modern language it has lost almost all conjugated forms. So – voida = to be able.