Actually that would typically be better suited to a card attachment IF your card has an external antenna connector. MMX or MMCX usually. You could put that on your AP (your wireless router) but the antenna you linked to is a directional antenna. If it were your only antenna then behind the direction it's pointed would have virtually no coverage at all. If you only have one wireless client and don't plan on adding nodes, at least not in the same general area as the existing clients then it might buy you something on your WLAn.
Ultimate a "cantenna" or any directional antenna would be used in a point to point environment, not a 360 degree WLAN coverage area.