It does have a currency, USD. I haven't had any issues using the card in the US and Canada (and if you travel to the States, it's more cost effective to use it there!).
Last time I tried, I couldn't transfer the USD gift card to my CAD registered Starbucks card online. But you could just try registering it in your account as a separate card? That should work fine. But, as @
IthinkIcan pointed out, you could try in-store too. Anyone have success with transferring a USD gift card to a CAD gift card in-store, or would they just register it as a separate card too?