Ephesians 1:3ff. pretty clearly teaches that, in some way or another, God “chose us before the foundation of the world,” and it even uses the word “predestined” explicitly.
How do Catholics understand this passage and other passages that use the word “predestination” or its variances?
A Catholic point of view of Ephesians 1 from the Haydock Bible Commentary
Ver. 1. St. Chrysostom takes notice, in his preface to this epistle, that the doctrinal part in the first three chapters is treated in a very sublime manner, with long periods and sentences, which makes the style more perplexed and the sense more obscure than in his other epistles. On this account I shall first give the reader a paraphrase as literal as I can, and then make some short notes on the difficulties in the text. (Witham)
Ver. 3. Blessed be the God, who, through his Son Jesus Christ, made man, hath blessed us with all spiritual blessings and gifts; and by his grace, infused into our souls, has given us a title to a happy eternity in heaven. (Witham) — In heavenly things; (in cœlestibus) i.e. all spiritual blessings for heaven, or for eternity. This is the object of all the blessings we receive from God; and we ought, according to the first intention of them, to refer them all to eternal or heavenly beatitude. St. Paul distinguishes the blessings which we receive in Jesus Christ from those bestowed upon the Jews, which were temporal and limited to this earth. (Calmet; Challoner)
[For additional comments on verse 3, see the Notes section, below.]
Ver. 4-8. As by his eternal decree, according to the purpose of his good will and pleasure, he hath made choice of us to be his adoptive sons, and predestinated us to be saved and glorified by the merits and grace of his beloved Son, our Redeemer, without any merits of ours to the glorious praise and riches of his grace, by which he hath made us abound in all wisdom and true prudence. (Witham)
[For additional comments on verses 6 and 8, see the Notes section, below.]
Ver. 9. That he might make known to us, and to all men, the mystery of his will and pleasure in establishing his new law, of calling all Gentiles, as well as Jews, to believe in his Son, made man for us, in the dispensation of the fulness of times, (that is, at the time decreed from eternity) to establish, to accomplish, and, as it is in the Greek, to recapitulate all things in heaven and on earth, in Christ, and through him, and his merits; on earth, by fulfilling all the types, figures, and prophecies concerning the Messias; and in heaven, by filling up the number of his elect. (Witham) — The mystery of his will. The word mystery signifies a secret, an unknown design. It was the will of God, to reveal to us the great design he had in the incarnation of his Son, viz. the formation of one great body of true adorers; composed, without distinction, of Jew and Gentile: till (ver. 10) when the time appointed shall come, he will reunite and perfect in or under Christ this one body, composed of the Church triumphant, Angels and saints in heaven, and the Church militant upon earth. (St. Chrysostom, Estius, &c.)
[For additional comments on verses 9 and 10, see the Notes section, below.]
Ver. 11. In Christ we also are called by lot; i.e. to this happy lot, this share and state of eternal happiness, (he seems to speak with an allusion to the manner by which the lands of a temporal inheritance was distributed to the Israelites, in Palestine) that we (ver. 12) who are saved, may be to the praise of his glory; might praise God for ever in the kingdom of his glory; particularly we Jews, who before hoped in the Messias to come, and also you Gentiles, who now having heard the gospel, have believed in Christ, and who, together with all Christians, have been now sealed as it were with the holy Spirit of promise; i.e. by the Spirit promised, and all those spiritual graces which are an earnest and pledge, which give us an assurance of our future glory and happiness. For our redemption from our sins, and in order to the acquired possession, to the possession of that glorious happiness which Christ, by his incarnation and death, hath acquired for us. (Witham)
Ver. 13. In whom you…were sealed, &c. Having been regenerated in baptism, you have received the Holy Spirit and the supernatural gifts which he communicates, by which he has, as it were, impressed upon you the seal of your sanctification and the pledge of your salvation. It is not an external impression, such as that by which soldiers are marked by their sovereigns, nor circumcision, as of old, but it is a mark within you—the grace with which you are filled—which shews itself outwardly by miraculous effects, &c. (Calmet) — Some refer these words, in whom you were sealed, to the sacrament of baptism; others to confirmation: both, with the sacrament of holy orders, confer a character, or mark, of which St. Paul seems to speak whenever he speaks of God sealing us.
[Ver. 14. See the Notes section, below.]
Not a very good idea 
So no, I don’t have anything to say about it. Surely somebody (or somebodies) will