I bought an electronic kitchen scale at Caynes in Toronto. They have an online store. Really any kitchen scale will do the trick. If you are shipping large parcels, you want to make sure that you will be able to see the read-out under your package or that the scale has a hold button to keep the read-out when the package is removed.
If you use Paypal shipping, you can get as much as 18% off some Canadian and US shipping rates, so I'd encourage everyone to check into it.
There is a Canadian shipping thread in the International team that is managed by an employee of Canada Post and has tons of shipping help. It's long but someone did an off-site summary that is helpful and you'll find the reference to it in the thread.
https://www.etsy.com/teams/7654/etsy-international/discuss/6779956/Jaime, I see that you are in the Toronto area. A similar service to the one mentioned in Montreal is Chitchatsexpress in Markham and Mississauga. I've been using them since June and have been able to reduce my shipping costs dramatically.