Learn Italian: Magari le Canarie fossero più vicine! - If only the Canary Islands were closer!

Because the Canary Islands are an archipelago (a group of islands), not a single small island. In Italian, archipelagos always take a plural definite article. Since Canarie is feminine plural, it takes le. By contrast, small standalone islands like Capri or Malta take no article at all.

Why is fossero in the imperfect subjunctive here?

The word magari at the start of an exclamation means 'If only...!' or 'I wish!'. When used this way to express a strong, unfulfilled wish about the present, it always requires the imperfect subjunctive.

Doesn't magari usually mean 'maybe'?

It can mean 'maybe' or 'probably' in other contexts, but when it introduces an exclamation followed by the imperfect subjunctive, its meaning changes entirely to express a deep desire or regret, translated as 'If only!'

Why does the sentence end with vicine rather than vicini?

The adjective vicine (closer) must agree in gender and number with the subject of the sentence, le Canarie. Because le Canarie is feminine plural, the adjective takes the feminine plural ending -e.