Going to Stockholm? Great choice! (Even though it's my second favourite big city in Sweden)
As mentioned above, we're not a part of the Eurozone so you might have to make sure to exchange some cash. Stockholm's not exactly a cheap city though when it comes to dining out/etc. I've not been to Canada (yet!) so I can't compare, but it is definitely more expensive than here in the US.
The subway/bus system is awesome and can take you within a few blocks of anything in town. If you stay, or visit, further outside the city there are also commuter trains that run fairly frequently.
We're pretty decent at English in Sweden, so the language isn't anything you have to be worried about during your visit. My significant (she's American) has visited twice and usually tries to practice the little Swedish she knows when talking to the locals. It doesn't work too well since the Swedes switch to English as soon as they can tell that she's American...
I guess I have a few suggestions of things to see/do (some that were mentioned above):
The Royal Palace:
They have some great museums here and they allow you take a stroll through part of the palace. They also offer tours but I've never been on an official one myself. I am sure that they have neat stories to tell but I just enjoy exploring myself. If you manage to time it, make sure to catch the guards when they change who is on duty.
http://www.kungahuset.se/royalcourt/...218000138.html
"Old Town":
The Old Town consists of the Royal Palace mentioned above and its surrounding areas. It is an awesome area to just stroll around and look at the quaint shops in the area.
http://www.old-town-stockholm.com/
http://en.wikipedia.org/wiki/Gamla_stan
The Globe Arena:
"Globen" is Sweden's national indoor arena and the largest (to my knowledge) hemispherical building in the world. The arena is primarily used for hockey, of course! You can take a tour in a globe up to the of the arena and look out over the city. They take a limited amount of passengers though so you'd probably have to book in advance for that. Just going there and seeing the arena is pretty cool though.
http://www.globearenas.se/en.aspx
The Vasa Museum:
Perhaps one of my favourite museums I've ever visited. The royal ship, Vasa, sunk on its maiden voyage in Stockholm harbor and was later salvaged and put on display at the Vasa Museum. Well worth your time if you're interested in history/ships/cool things.
http://www.vasamuseet.se/en/
Other things that might be worth your time:
Kaknästornet (
http://www.kaknastornet.se/eng/)
City Hall
Skansen (the zoo)
If you want ideas on what to do, this site seems promising:
http://www.visitstockholm.com/en/