"I have no idea whether the prices include import/export duties or any other handling fees."
KISS
Get a price for USPS (postal service) www.usps.com
Using the ZIP code for city hall in St Paul and Winnipeg, USPS gives me a cheapest cost of US$ 178.50 (appx Cdn$ 232)
Tax and Canada Post fees on a US$100 (Cdn$130) item imported from the USA into MB will be about $28 (GST+PST+CP fee) if the item is considered "duty free"
So total shipping and tax and fee will be about Cdn$260 using the mail (add duty if not manufactured in North America)
FedEx and USPS would cost a lot more
" it appears there's no import charges (NAFTA)"
As stated earlier you will be charged GST and PST at time of Customs clearance just as if you had purchased the item at a local retailer in Winnipeg. Canada Post will also charge you a flat $9.95 handling fee. There will be no duty charged since the item is USA made and comes into Canada "duty freee" under NAFTA.
http://www.cbsa-asfc.gc.ca/import/postal-postale/duty-droits-eng.html
Hello 'izaquarius',
<<I'm trying to figure out how much it would cost my brother (in the US) to ship an item to me (in Canada).>>
Ah, I see. It seems like a small detail but it actually clears a lot of things up. Americans have a 4 pound, 36 inch ttl
limit on what can come cheaply through First Class Mail, -- after that it is Priority and that is quite costly, especially
for a 30 lb package.
You brother would go to the USPS site here to find shipping to Canada:
https://ircalc.usps.com/?country=10054
He will need postal codes, that will be easy because you and he already know each others codes. I tried it with
City Halls of both Winnipeg and Minneapolis.
He enters the item's value (100), chooses Large package, clicks Continue,
then enters the postal codes, the length - height - width, (I used your 24 - 15 - 8),
and then looking for the Priority Mail International Options hidden under the costlier Express choices, the cheapest
figure I see is $113.45 US.
Have you seen this link about importing things into Canada by mail? At the moment, anything with a declared value
over $20 is subject to charges.
http://www.cbsa-asfc.gc.ca/import/postal-postale/duty-droits-eng.html
Unless it is a gift valued at $60 or less, but I'm not sure if speakers - even from your brother - would qualify:
http://www.cbsa-asfc.gc.ca/import/postal-postale/gifts-cadeaux-eng.html
I don't suppose he'll be driving up to see you any time soon? Canadians can bring back up to $200 worth without charges
if they are driving. It's still not a huge amount for a shopping trip, but better than 20.
Shipping a package of that size and weight will not be cheap, but couriers always charge for values over $20 and
you'll pay hefty brokerage fees to have them do it.
Items that come through the post (at least those with a low value, say, under $100) are often not assessed. Do not
count on that and be prepared to pay, but the most Canada Post charges is $9.95 for processing, plus whatever taxes
and duty the item has incurred.
Talk to your brother and see what he thinks. And decide if the total cost, especially that shipping fee (which you will
ultimately have to pay in Canadian dollars) is worth it.
Try not to think of it in terms of shipping costs, but if the total price is a fair price to pay for the speakers you want.
And if you are wondering 'roughly' where the exchange rate has the dollar at any given day, this here is my favourite
link, but you might find one you like better:
https://ca.finance.yahoo.com/currencies/converter/#from=USD;to=CAD;amt=1
I wish you all the best with it. 
If you take a look at the UPS site, you will see the charges for import clearance (brokerage fee)
https://www.ups.com/content/ca/en/shipping/cost/zones/customs_clearance.html
On top of the page you will see: Note: Rates do not include applicable duties or taxes.
The brokerage fee for Cdn$130 item (US$100) is $26.60 (compared to $9.95 by Canada Post)
In addition, look at the bottom of the page carefully. COD charge will be added (for the driver to collect the money from you) so will disbursement charge (for UPS paying the tax to the government on your behalf) Canada Post does not charge for these. All services included for $9.95.
Other carriers (Fed-X etc...) have similar charges
To avoid these charges with carriers, one must select more expensive services where the shipping charge is increased to take care of it. In all instances, Canadian taxes are always extra.
Good Luck.
