It seems geographically impossible,they have the baltic between them and different interests.
Sure russia is a common foe but that was more an on-off thing,also sweedes probably dont care at all about defending polish lands and i dont expect poles to eagerly march across finland.
All in all it just seems horribly impractical,sweeden has a lot more to gain by concentrating on scandinavia and not getting dragged into anymore pointless wars,poles on the other hand are also to large to accept foreigners to rule them without any existential threats,especially given such foreigners dont have large means to enforce that claim.
If we compare it to the polish-lithuanian commonwealth or the habsburg monarchy(later austria-hungary),in both cases they basically covered each others backs so to speak and were in the same general geo-political situation and the alternative was being taken down seperatly by their enemies,the poles with the sweeds have no benefit of effective border cover and all the problems of being in a union with another large nation,mainly common wars and foreign attempts to enforce unity.