This indeed is a wish (attainable) = "un souhait réalisable". I understand your perplexity: its cause is probably that there is an inversion in the English sentence: "may my life be..." But if it were a question, there were "is my life guided..." or "can my life be..." and a question-mark. The original Portuguese sentence begins with a "Que" and the verb is in subjunctive mood "seja" (It. "sia", Fr. "soit"
, these indicate it's a wish like in a prayer. In French, both of these constructions can be used: Que ma vie soit guidée par ma foi et mon amour en Jésus-Christ!
Puisse ma vie être guidée, etc.
In a way (I'm not sure of it) MAY stands here in English for subjunctive. Perhaps in old times, it could have been : Be my life guided...
How would this be expressed in Polish (subjunctive?)?
Last thing: you've put "posset" in imperfect subjunctive. It implies that wish is unattainable (hence a regret). It needs present subjunctive to indicate life *can* be guided..., despise the "peccatum originale"! Otherwise we're in heresy...