As they're usually in small units 5-10. Which means you can usually be steadfast against them, and a small frontage can reduce the number of incoming attacks, so you could get them with combat res.
Their large base size, and normal Movement, means they are a bit unwieldy like a horde, so you can try and manoeuvre them where you want them.
Handgunners, and or a volley gun can soften them up a little bit first. As Naitsabes said, Cannon in the Flank is nasty. Luminark Laser bound spell in the flank could possibly do so damage as well, not as reliable as a cannon shot though.