Well, technically you can do anything you want for a movie adaptation. If your Black Canary would use guns in that instance, then your Black Canary would use guns in that instance. Just be aware that it is a departure from the comics.
Even the comic book Black Canary would occasionally use other sorts of weapons, though, if you think that would make for a cool scene. Staves, swords, kamas, kukris, katanas, nunchakus, sais, even spears or nagintas; basically anything Asiatic or relating to the martial arts.
Something that would be sort of an appropriate "in-joke" would be the crossbow; Black Canary has been often partnered with Huntress in the comics, who does iconically use a crossbow. Having Dinah use a crossbow in lieu of Helena would be a sort of wink at the comics-reading audience.
As a final note, just be aware that the comic book Canary Cry is very powerful; shattering walls, knocking sht over, powerful enough to give most supervillains pause. If it doesn't hurt a villain when something like guns will hurt the same villain, there should be a fairly good reason for it, otherwise it's another departure from the comics. Which is fine as long as that's what you want.