Amour being a masculine noun, you should use ‘bel amour’ regardless of context.

Amour is one of those words that are masculine in the singular and feminine in the plural. In Old French feminine was used in the singular as well.
Nowadays we only use the masculine in the singular in everyday language but poetic licence can allow you to do lots of things, and you’d not be the first one to use belle amour in the singular. Ma belle amour is a French song by Quebecois singer Michel Rivard. La belle Amour is the title of a song by French singer Barbara. Belle Amour is the name of a shop that sells wedding dresses (no commercial link but you can easily google it). La belle amour humaine is the title of a book by Haitian French speaking writer Lyonel Trouillot. And we’d probably find plenty more.
So there’s absolutely no reason why you couldn’t name a film Belle Amour. Although you might prefer Ma (or Une) Belle Amour since orally Belle Amour would sound ambiguous and most people would take it down in writing as Bel Amour which is not what you want.

Beautiful love would translate to bel amour but, as a title, bel amour alone would be more suitable for a person, which is not what you want.

By contrast, Un bel amour is more suitable for a love story.

In any case, it does not matter if it is spoken by a man or a woman.